I wrote a custom c# add-in that uses the API and worked great when we were using SW2016 SP5.0. However, when we updated to 2018, I started encountering strange errors that are causing some calls to break.

I can't wrap my head around the reason for this error or a potential fix.

Scenario:

I have a drawing open. I click export on my add-in to output a STEP file. The add-in goes through the print to find the referenced document file path and then calls ActivateDoc3(Name, UseUserPreferences, Option, ref Errors). None of these variables are null or incorrectly formatted.

Error:

ActivateDoc3 Error

Could not load file or assembly 'gdtanalysissupport, Version=11.37.0.0, Culture=neutral, PublicKeyToken=[a bunch of numbers]' or one of its dependencies. The system cannot find the file specified.

The 3D referenced file does not open and causes further issues. I don't know why that DLL is being called nor do I know why it can't find it. It's located in my installation folder, right where it was installed. Has anybody encountered this or have any suggestions?

I know it's usually best to supply code and example files but neither of those are options and I can't recreated this with every file unfortunately. It only happens to some so I can't create a test file and repeat it.