System.IO.FileNotFoundException: Could not load file or assembly 'X' or one of its dependencies when deploying the application

Solution 1:

... Could not load file or assembly 'X' or one of its dependencies ...

Most likely it fails to load another dependency.

you could try to check the dependencies with a dependency walker.

I.e: https://www.dependencywalker.com/

Also check your build configuration (x86 / 64)

Edit: I also had this problem once when I was copying dlls in zip from a "untrusted" network share. The file was locked by Windows and the FileNotFoundException was raised.

See here: Detected DLLs that are from the internet and "blocked" by CASPOL

Solution 2:

I resolved this problem by renaming the DLL. The DLL had been manually renamed when it was uploaded to its shared location (a version number was appended to the file name). Removing the version number from the downloaded file resolved the issue.