MS Access + IIS + Impersonation ='未指定错误'？

I have an ASP .NET (2.0) app that connects to an Access database over a network share using impersonation and basic authentication in IIS. Everything was working fine up until today, when I started getting weird 'Unspecified Error' error messages. I ended up doing an IIS reset to resolve the problem, but I'm trying to figure out why it may have happened in the first place. I have an ASP .NET (2.0) app that connects to a