On a fully working 2013 SP1 dev environment, we have just installed the legacy pack and upgraded a legacy CM database containing VB script templates. We have replaced the legacy event system with a .NET rewrite, which consists of an Events dll and a referenced Common dll (which in turn references log4net.dll) all of which sit in the Tridion/bin folder and the Tridion/webservices/bin folder.
After shutting down the Tridion COM+ process, when I preview a page which uses a VB script template, I get an error:
Error: Could not load file or assembly 'Example.Project.Common, Version=188.8.131.52, Culture=neutral, PublicKeyToken=abcdefghijklm' or one of its dependencies. The system cannot find the file specified.
Note that this error is only shown in the GUI and not in the Tridion event log.
If I ignore the error and re-run the preview, it works fine. It also works fine if I disable my .NET event system. Previewing Modular templates works fine, and also my events are all executed just fine. On another environment without the legacy pack, I never see this error (but I dont have any VB script templates on that environment, so I cannot reproduce the same conditions).
This all seems properly weird to me as the preview does not have anything to do with the event system (no events are triggered when previewing). Does anyone have any clue as to what might be happening here???