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Did not find the metadata file netstandard2.0 dll

What does it mean that visual studio did not find the metadata file netstandard2.0 dll? This file should will be on the bin folder so it should be automaticly created by xamarin by compiling the code.
Also it waring the depencences. Why is it? How could I solve this?

Please follow the steps below to check if it is helpful to you.
Right click on the solution and click Properties.
Click Configuration on the left.
Make sure the check box under "Build" for the project is checked. If check then uncheck and check again and save the settings.
Clean the solution by right clicking on the project solution and rebuild the project again.
Make sure you don't have any other error messages in your project and if you do, fix those first.
I have got this solution from this link Click here
if this solution does not work for you please follow the steps below
1 - Close the solution
2 - Delete obj, bin folder for PCL, android, ios project
3 - Open solution and build

ASP.NET project reference not found...at all?

Above are the problems I am having right now, and I can't contact the old programmer. The AjaxToolkit is referencing to him and I have no idea where to change that reference. Or where to get that exact part of the Toolkit that it's looking for.
TL;DR:
Check the link.
Where do I change this reference?
Where do I find AjaxControlToolkit-Framework3.5SP1\AjaxControlToolkit\ExtenderBase\ExtenderControlBase.cs?

You can change the path of your references in the .csproj file
PS : To open up your csproj Right click on your project from your IDE > Open Folder In Windows explorer > You can find a file with csproj extension > Edit with notepad

how to import dll in c#

I have some .dll and .xml(e.g. FarsiLibrary.Resources.dll ,FarsiLibrary.Resources.xml) to use with Persian calender .
how do I import it in my project.
note: I'm using Visual Studio 2012.

"Right click on project -> Add Reference -> Browse..." for DLL.
Add existing file for XML.

You just need to do following
Right click on your project and choose Add Reference.
When the dialog comes up, choose the Browse tab and go find your dll
After adding the assembly include that reference in your class or
form where ever you are going to use
Or you looking for [DllImport("dll")]? More Here

Microsoft.SqlServer.Management.SqlParser nedded in clickonce

I want to make a click once via ftp, after deploying the project and excute I have Microsoft.SqlServer.Management.SqlParser V 10.0 needed .
I have installed 1033\x64\SharedManagementObjects.msi Version 10.50.2500.0
but I can't found this file in the sdk directory ! and the other thing that I don't use this dll in my sollution !
How can I resolve this?Any sort of help will be appreciated.
Thanks

Probably a dll that you use in your projects needs it and it is using it from the GAC. In your deployment machine there is no such dll. Open your project properties and click on "Publish". Click on "Application Files" button, and check "Show All Files" in the opened dialog. See if the missing dll is there and change its publish status to "Include".

Cannot Edit or Add Path to Reference File in Visual Studio 2010

Cannot Edit or Add Path to Reference File
, I cannot edit or add a path to a referece file. I have inherited a project at work. When I open the project and go to the references scetion in the Visual Studio 2010 IDE there are some little yellow warning signs showing that there is something amiss with the reference listed there.
But when I click on the item and look at the missing path, I find that the name "Path" is in grey suggesting that I cannot edit it and, sure enough, I cannot add the path name to the adjoining field. What causes this? I have the solution file and the project file checked out in edit mode.
When I open the project file, the error list also gives the warnings for each missing reference:
"The reference component '(the file name)' cound not be found"
Well, I know where they are but editing the path to point there is the problem.

I think in this situation you've got 2 choices:
Remove the broken references and re-add them to the project - this is easy to do if you don't have too many broken references.
Right click on the project file in Solution Explorer and select 'Edit Project File' and manually fix the reference hint paths (the project file is XML). Save, and right-click the project file in Solution Explorer again and select 'Reload Project'.

Editing the project file by hand found the problem.
THe project file is an xml file.
It did not take long to find a reference in the path that was wrong.

I had the same issue, none of the above solution worked. Only thing I was supposed to do was right click on my sln file, click on "Enable nuget package restore option", save it, close the visual studio. Open it again, clean and rebuild the solution. Visual studio rebuilt the solution successfully.

I also had a problem with adding references
i would add a reference and the path is always empty
what eventually helped was
Right click project > unload project
Right click again > Edit project file
in project file scroll to bottom and remove group named:
<Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">
....
</Target>
reload project again and build