One other question - this DLL has some function that writes a file to disk. The DLL is loaded by the DotNetGatewaySS.exe process (or 64 bit.exe version). That executable was spawned off by Cache.exe and takes the same user name on windows. What's the user listed in task manager? Do they have write permissions in the folder you're trying to write to?
I saw that too but we ran into this when upgrading to 2.2.1, the current version of Wireshark. I think it is still an issue.
Laura, can you give some details about the versions you are using here?
Cache server version? Bitness?
your DLL - what .NET framework version?
The .NET gateway configuration has a few settings you can change before starting it, like 32 or 64 bit and the .NET framework version. Can you screen cap the .NET gateway settings page from the portal?