Recently a client found they could not save changes to a customized form in CRM 2011 Online.
The client had created custom versions of the Account and Opportunity Main Forms and assigned permissions. They had then added custom fields and java script to the new forms, saved and published. Sometime later they attempted to move some fields around and received the following error when trying to save the form:
Microsoft Support did not find the reason but claim they are continuing to investigate. Their work around was to delete and recreate the custom forms.
Our solution: Save As.