Document error in log - Bad subpanel definition

When I go to Documents and open Document I have this error in log:

Tue Nov 4 03:34:13 2014 [1503][a2cc3e71-e86b-c13d-8800-543fbbaa0a18][FATAL] Bad subpanel definition, it has incorrect value for get_subpanel_data property aos_contracts_documents

Is this a bug?

What version of SuiteCRM are you running? Have you tried running a Quick Repair & Rebuild and executing changes once complete in Admin -> Repair?