For years now I have been recommending that SolidWorks users not create VSTA macros for serious use in their production environment. Running a VSTA macro from the VSTA is fine, but running the macro from the DLL has historically given me and many other users problems. For example, here's a couple of the errors I've received either on my computer or on other users' computers. Particularly the latter.
Cannot open DLL:
Microsoft Visual Studio Tools for Applications has encountered an error. The primary host process unexpectedly shutdown.
A few others have documented their experience here:
Is there anyone here who is using VSTA macro DLLs successfully on other users' computers?