Unsigned assemblies and application running from NAS

I created an in-house utility program that we run from a NAS location. This program loads several unsigned DLLs at runtime (LoadAssembly). The program runs fine most of the time, but from time to time, a user will get a SystemAccessViolation exception (trace shows a call to StrongNameSignatureVerification as the last thing that happened).

I'm not sure exactly what is going on. Multiple users can be running the program. Like I said, the program runs most of the time.