this is being caused by a bug I have just identified in form builder.
you have form elements that have a comma in the name, for example:
the name of the form element is generated from the label you apply to it in Form builder. If you use commas in the form element label, they will also be applied to the name. Commas in the form element name are not legal.
For now, please don't use commas in the element labels. I have logged this as a bug in our bug base to have it fixed in a future update.