Could not load file or assembly. The system cannot find the file specified.

Error:

Error while loading code module: 'MyDLL, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. Details: Could not load file or assembly 'MyDLL, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified.

Resolution:

If you use custom DLL in your SSRS reports, make sure the DLL is copied over to the shared DLL folder.

For VS2017 Community Edition, copy over the DLL to this folder…

C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\IDE\CommonExtensions\Microsoft\SSRS

Other Locations:

C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\Common7\IDE\CommonExtensions\Microsoft\SSRS

C:\Program Files\Microsoft SQL Server\MSRS13.MSSQLSERVER\Reporting Services\ReportServer\bin

Sources:

https://stackoverflow.com/questions/43520437/ssrs-custom-assemblies-could-not-be-loaded-under-visual-studio-2017