New answers tagged gac
Here is the link for grabbing all installed SharePoint solutions. If you don't explicitly need the associated assemblies, it should suffice.
The DLL you are trying to add is most likely a 32-bit DLL. SharePoint development is done in 64-bit and thus it is not possible to use that DLL in your application. That also explains why SharePoint is not able to load your DLL since you only have the 32-bit DLL installed in your GAC after deployment.
Top 50 recent answers are included