When loading an ASP.NET 3.5 web application that has been compiler for Any CPU onto an IIS7 server I got the error

The ‘Microsoft.Jet.OLEDB.4.0’ provider is not registered on the local machine.

This was because the server was running a 64bit OS and only the 32bit Access Driver was installed. The quick fix to get this running was to enable 32-bit applications on the AppPools advanced settings.