Is it possible your form is getting double-submitted? After you see this error message, can you check to see if the entry has been saved on the entries page? If not, I think I'll need to take a look at the form. Can you provide a link?
As for the Chrome submit button, I'm guessing you have required fields that are hidden. Chrome doesn't allow the form to be submitted if any required field is blank. There will be a beta version available within the next couple of days, but for now you can open formidable/classes/controllers/FrmFieldsController.php and change line 230 from this:
echo ' required="required"';
to this:
//echo ' required="required"';
P.S. For faster support, please post in the Pro forums.