Could not load file or assembly for project reference, reference dlls vs csproj [duplicate]

Solution 1:

I am pretty sure you're having a 32-bit / 64-bit conflict. It sounds like your main project might be set to 32-bit while the class its referencing is set to 64-bit. Try looking at this SO question and this one too. Between the two of them, you should be able to figure out your problem.

Solution 2:

Might be you are facing the problem with your website after deploying on server.

Then you need to adjust your application pool to Enable 32-Bit Applications.

Steps

1. Open IIS Manager
2. Click on Application Pools
3. Select whatever application pool you are using

4. From right pane, click Advanced Settings...

5. Set Enable 32-Bit Applications to True

   

Solution 3:

I just had this error message running IIS Express in Visual Studio 2015. In my case I needed to be running the 64 bit version of IIS Express:

Tools → Options → Projects and Solutions → Web Projects
Check the box that says "Use the 64 bit version of IIS Express for web sites and projects".

Screenshot:

Solution 4:

I had this same problem. I had set Project A's "Platform Target" ("Project A"(Right Click)->Properties->Build->"Platform Target") to x86 but kept Project B's at "Any CPU". Setting Project B's to "x86" fixed this.