The rest of the error message is: "One or more required custom controls in this form cannot be created".
I also get this message when clicking the Edit This Task button on the Workflow Task toolbar in MS Word 2007 when I am part of a Collect Feedback workflow.
I do not understand even what the form is it is talking about. Has any of you guys experienced this?
We have SharePoint 2010 and MS Office 2007.
Also see MSDN Forum.