In MOSS 2007, we could update the tag's callstack attribute to true and then customerrors mode to "Off" to see the actual error behind the 'An unexpected error has occurred' message. Does it apply on SharePoint 2010 as well ? I tried it but I get the following error:
Runtime Error Description: An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed.
Details: To enable the details of this specific error message to be viewable on the local server machine, please create a tag within a "web.config" configuration file located in the root direc...