I believe I have a problem similar to this one. Mine is not in the Field Services module, however, I am receiving this message when I try and update an activity for an opportunity:
Please make sure an input control for 'Name' is on the screen and a value is entered.
Additional Information
Action Sequence Order:9
All required fields on the screen have info in them. I am new to the customization on this program. In creating a new opportunity screen I changed some fields in the opportunity table. I don't believe I changed any others but may be forgetting some. I changed the Tab to point back to the original opportunity screen, however, the error is still there which leads me to believe its an error from a table (sorry if that is an obvious assumption). It seems to give this error when Save Opportunity or Save Opportunity, Activity, & New Activity are pressed. Maybe I need to have a list of the original tables and required fields as they were.
Any ideas on where to check for this?