File or assembly name not found follow up.
So, we finally figured out a problem a customer had with Microsoft's help. As posted below the customer had random errors where a temp file that was generated by .NET (confirmed by Microsoft). We ended up using filemon to log disk access while the error occurred, and the culprit was FreeTextBox. We don't use FreeTextBox (although it is a great editor), but somehow it was in the bin directory on the clients server. After we removed that dll the problem went away. If we had been using it, the solution would have probably been to add it to the GAC. If you ever run into this, use the method above as it's more than likely permissions and you'll know pretty quick whats going on with filemon from sysinternals.