the problem is with a datepicker.

you very likely set datepicker's value but your source is NULL or not recognized as valid date.

Agreed. Check all the settings for any date controls. You can also readd them to the form and connect them to the appropriate list column.

Also, do you have any custom JavaScript on the form?

Thanks, I believe that I had originally used the date in a calculation, then deleted the calculation, but for some reason it was still being called in the form.  I checked everything in the form and couldn't find any reference to the field that was being referenced in the error message, so I finally ended up creating the form over from scratch, this resolved the issue.