When an error occurs within Microsoft SharePoint Foundation 2010 a Correlation ID will be displayed in the error message:
This Correlation ID is logged within the SharePoint log files and you can use it to find out more details about the error that occurred.
The two pieces of information you will need from the error message above are the Correlation ID and the date and time of the error.
Once you have those two pieces of information, browse to the SharePoint log files on your SharePoint server located at:
C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\LOGS
The log files will be labeled with a date time stamp so find the one that corresponds to the time frame of the error and then open this log file in Notepad (or the text editor of your choice) and search for the Correlation ID.
You will probably find it listed in several places, from the beginning GET request to when the error occurred, and finally to when the logging of correlation data stops. Of course you are probably most interested in the error message but there will be more information in the log associated with the Correlation ID to help you find the root cause of the error.