Hey,
Thanks for the quick responses on this. I had tried the form redirecting and reloading and these both had no effect on the outcome.
The error occured when the user copied the form from an existing form and had a field that didnt exist in the form builder, after they had updated to suit their needs, and was referencing the old form field in the Auto Response section of the form.
This was resolved when i created a new form from scratch and informed the users to do the same moving forward.
Thanks again for the help!