I'm getting this same error message. I haven't been able to figure out what is causing the error. What led you to believe it is due to too many characters in a certain text box? I've been trying to figure out how to backtrack to the item/field in the form that is causing the error, but of course there are no details in the error message.
What's odd is I don't get any error when testing the form using 'preview' in the client. I only get this error once I've published the form to SharePoint & test from there.The form is browser-compatible with no errors when I run the design checker.
Any help is appreciated!!
Thanks,
Megan