Have a useful tip for you developers out there. As you know the SharePoint "error" page is not very good about indicating what has happened when an error has occurred - while good that the user's don't see it, it is pretty frustrating when developing.
To get around this issue requires a few updates to the Web.Config file in the site you are working with. Of course, the first is that the site be enabled for debugging - locate the line:
and change it to:
This will allow you to debug your project; however, to get the messages, do the following two steps (both of these are done in the web.config file):
1) Locate the line: callstack="false" and change it to: callstack="true"
2) Locate the line: customerrors="on" and change it to: customerrors="off"
Save the web.config file, run an IISReset and you are good to go.
NOTE: Don't ever do this in a production environment lest your users see complete (raw) error messages.