If you work with ADFS, you get pretty used to the error box with a GUID reference number. So what is this mythical number? It’s a reference to the Windows Event Viewer. To see these GUIDs: refer ADFS v2.0 : Finding errors referenced by the reference number.
To quote @Marnix in the above link:
“Open the Event Viewer. Navigate to 'Applications and Services Logs' -> 'AD FS 2.0' -> Admin. In the 'View' menu, using 'Add/Remove Columns...', add the 'Correlation Id' column. Look up the reference number “xxx” in the 'Correlation Id' column.”