I came accross an error in one of my infoPath form templates.  I was working on a template and able to save and publish to the form to SharePoint.  A blank from can be opened and submitted using the published template in Sharepoint, but if I try to edit (design) the template, the following error occurrs when InfoPath is attempting to open the form:

 

 

There are a number of possible causes for this and similar (parameter) errors, but in this case the error was caused when I removed dome empty group elements from the form’s main data source.  The groups were no longer being used on the template and did not contain any fields so I would have assumed that thay could be removed without issues.  I was able to narrow down the cause by retracing my steps using previous (working) versions of the form template.

 

For more details, see InfoPath Error When Opening Form Template in Design Mode.