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Could not load file or assembly 'System.Collections.Immutable' but i don't have any references to it

I'm on V16.4.1 and the project is targeting .NET Framework 4.7.1
I have a solution with multiple projects which all run fine except one which gives the above error. I searched the project and can't find any using references to it and just in case, I added the dll to my references. I searched the entire solution in case I was referencing it through another project but there is no reference to it anywhere
I tried deleting bin & obj folders. Cleaned and rebuilt the project but I get the same error every time.
Edit: The project can build, this only happens when I try to debug it
bin\roslyn\csc.exe is throwing the exception
Could not load file or assembly 'System.Collections.Immutable,
Version=1.2.3.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or
one of its dependencies. The system cannot find the file specified.

I use
Visual Studio Professional 2019 ver 16.7.6 / Preview: 16.8.0 Preview 4
and I found the same problem with many 'old' project using .net framework when I compile them from scratch (i.e. deleting bin/obj directories).
The compiler does not recognize that the runtime needs this package, and the solution is to copy in the bin directory the requested version (1.2.3.0 in this case) of DLL System.Collections.Immutable.dll
You can download it adding this line to packages.config file:
<package id="System.Collections.Immutable" version="1.2.3.0" targetFramework="net471" />
but still need to manually copy the .dll in bin directory.
Or add the package with Nuget.

Stefano's answer worked for me
this file is a dependency from my firebase dll, tough i didn't need to modify packages.config because the file exists in my bin folder
I just included System.Collections.Immutable.dll file in in VS project
then changed in file properties > advanced > copy output > copy always
thanks!

errors CS0246, CS1504 and CS2015 when trying to compile through csc [duplicate]

I am trying to make a simple c# program using Growl C# API.
I tried to compile my program in two different ways:
1) I kept my .dll file in the same directory as my .cs file. Than I ran
csc /r:Growl.Connector.dll,Growl.CoreLibrary.dll /out:test.exe *.cs
It compiled fine and also ran fine.
2) Now I have created a directory inside my current working directory named growl and kept all my .dll references there.
Now when I try to compile it using the below command
csc /r:"D:\Modified\Growl_NET_Connector_SDK\libraries\growl\Growl.Connector.dll","D:
\Modified\Growl_NET_Connector_SDK\libraries\growl\Growl.CoreLibrary.dll" /out:test.exe *.cs
It compiled fine but when I tried to run it the below mentioned exception occurred.
Unhandled Exception: System.IO.FileNotFoundException: Could not load file or assembly 'Growl.Connector, Version=2.0.0.0, Culture=n
eutral, PublicKeyToken=980c2339411be384' or one of its dependencies. The system cannot find the file specified.
at GrowlNotification.Program.Main(String[] args)
So, my question is what is the correct way to reference .dll file in csc when files are in an external folder.
Here is the directory structure for 2nd case.

So, my question is what is the correct way to reference .dll file in csc when files are in an external folder.
You're already referencing them at build time. You just need to make them available at execution time too, but copying them into the same directory as the executable, when you want to run it.
You could also investigate using the Global Assembly Cache if these are signed assemblies, but personally I'd stick with just keeping the executable with the libraries on which it depends.

You can add these using the /lib and /reference command-line switches while compiling.
http://msdn.microsoft.com/en-us/library/s5bac5fx.aspx
But (Quote from the article)
An alternative to using /lib is to copy into the working directory any
required assemblies; this will allow you to simply pass the assembly
name to /reference. You can then delete the assemblies from the
working directory. Since the path to the dependent assembly is not
specified in the assembly manifest, the application can be started on
the target computer and will find and use the assembly in the global
assembly cache.
Because the compiler can reference the assembly does not imply the
common language runtime will be able to find and load the assembly at
runtime. See How the Runtime Locates Assemblies for details on how the
runtime searches for referenced assemblies.
so Jon Skeet's answer is better. (I'm just adding this to provide more info than I could in a comment, not as an answer. Jon's answer is the best IMO)

You can create symlinks to the assemblies in your libraries folder so you would only need to keep them updated in one location.

d3dcompiler_47.dll, ILMerge failing. Also wont add to GAC. Any Idea?

Goal: I need all the files in my bin to be grouped into a single dll. or added to the GAC
I am using CefSharp To run chromium in a windows form.
We are using some software that will only allow me to add one dll (no other files).
I have access to the GAC on all machines. And I have been using ILMerge to attempt to bundle the files with the dll.
I have been able to get all the files to bundle except for. d3dcompiler_47.dll
When I try to add to GAC it tells me it has a bad manfiest.
When I try to bundle d3dcompiler_47.dll with my dll, it says
"System.BadImageFormatException: Could not load file or assembly
'd3dcompiler_47.dll' or one of its dependencies. The module was
expected to contain an assembly manifest. File name:
'd3dcompiler_47.dll' ---> System.BadImageFormatException: Could not
load file or assembly 'd3dcompiler_47.dll' or one of its dependencies.
The module was expected to contain an assembly manifest. File name:
'd3dcompiler_47.dll'"
(I have reviewed this but found that its 2 versions of d3d... do not work with CefSharp)
api-ms-win-core-libraryloader-l1-2-0.dll missing when d3dcompiler_47.dll is redistributed
Is there anyway to add d3dcompiler_47 (from CefSharp) to bundle or be added to the GAC?

As Hans said, you can't use ILMerge for unmanaged dlls.
Fody Costura however should work, at least it says so in its features.

Assembly's definition does not match

Error 2 Could not load file or assembly
'CrystalDecisions.Enterprise.Framework, Version=10.2.3600.0,
Culture=neutral, PublicKeyToken=692fbea5521e1304' or one of its
dependencies. The located assembly's manifest definition does not
match the assembly reference. (Exception from HRESULT: 0x80131040)
Can anyone tell how to correct this error?
I tried to delete the files from the bin folder and I even tried downloading a new dll file and added reference to it. Still it didnt work out.

The solution was pretty simple. Just delete the assembly and associated files from my projects bin folder and then choose Add Reference to add the latest version back in.

This can be due to your project file referring to one version while the version copied into the bin folder is a different one. So when the app runs it's trying to load the version the project file references, but finds only the one copied into the bin folder.
Was the library added through Nuget? It could be that the version in the referenced in packages.config and used in the build doesn't match the version number in the project file.

PRISM: referencing DLL's in the main Project that Module depends on

I am getting this exception in the main Project PrismDashboard:
Source\PrismDashboard\bin\Debug\PrismDashboard.vshost.exe
System.Windows.Markup.XamlParseException occurred
HResult=-2146233087
Message=Could not load file or assembly 'Microsoft.Expression.Interactions, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.
This is the project with Bootrstrapper and Shell. It is happening because Shell is using ModuleA from another Project:
Source\Modules\ModuleA
That requires refrence to Microsoft.Expression.Interactions and I can see that this DLL exists in:
Source\Modules\ModuleA\bin\Debug
I'm not getting compile error, and I'm getting runtime error.
ModuleA View will be injected into Shell Region, and this View requires Microsoft.Expression.Interactions which is referenced in ModuleA project but not in the main Project with Bootstrapper and Shell.
I don't want to add reference to DLL's required by other projects in my main project.
Have tried to set Embaded Interop Types on reference in ModulaA but getting error:
Error 1 Cannot embed interop types from assembly 'c:\Program Files (x86)\Microsoft SDKs\Expression\Blend.NETFramework\v4.0\Libraries\Microsoft.Expression.Interactions.dll' because it is missing either the 'ImportedFromTypeLibAttribute' attribute or the 'PrimaryInteropAssemblyAttribute' attribute c:\Program Files (x86)\Microsoft SDKs\Expression\Blend.NETFramework\v4.0\Libraries\Microsoft.Expression.Interactions.dll ModuleA
Error 2 Cannot embed interop types from assembly 'c:\Program Files (x86)\Microsoft SDKs\Expression\Blend.NETFramework\v4.0\Libraries\Microsoft.Expression.Interactions.dll' because it is missing the 'GuidAttribute' attribute c:\Program Files (x86)\Microsoft SDKs\Expression\Blend.NETFramework\v4.0\Libraries\Microsoft.Expression.Interactions.dll ModuleA

The main application needs to be able to find Microsoft.Expression.Interactions in order to load module A, no way around it. Also keep in mind when you distribite your application the same rule applies.
If you really don't want to reference that assembly in your shell project (which btw is actually the easiest way since it will copy it to the main application's output dir so you're settled) the only other option is copying it there manually. Could be done using a post-build event, but by doing that you're also tieing both projects together since they need to know about each other's output directory. Another way is making all projects put their output in the same directory. I'v been using that for some pretty large scale applications and it works nicely. Also distributing the application is then just a matter of copying that entire directory.