Investigating SharePoint 2010 Errors
In SharePoint 2007 finding more information on exception errors generated by SharePoint was not easy. It generally involves noting the time at which the error occurred and trawling through the log files looking for exception information. This is now much easier in SharePoint 2010.
When an exception is generated, the error dialog is displayed:
Each error dialog has a unique correlation id (GUID). You can search in the error logs (C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\LOGS) for this correlation id to locate more information on the error.
Note: SharePoint Log files are now compressed by default.