Sometimes Force.com IDE would throw such generic error when trying to save to the server, the error mentioned is "An unexpected error has occurred". Right, that's helpful... The Log Viewer will have "Save failed!(Open log file for full message and/or stacktrace" and I never found a good way to "open log file" other than checking the debug log from the Web UI (Admin Setup > Monitoring > Debug logs). Mostly I found the error is the result of using field values without including them in a query, or a failed System.assert call. Why couldn't the IDE just say so? There are a host of other things that may cause this too, which makes debugging a pain.