Error Occurred While on Success Script

Error Occurred While on Success Script

Users are reporting this error on one of our embedded forms [Note to support: it's the "Hell's Kitchen" form]. 

The rest of the error message isn't very helpful:

"We are working on giving more meaningful error messages on script failures".

What are we supposed to do with that..?

The user in question received this error 4 separate times, waiting 2 hours between each submission.

I have enabled support edit access. We need to address this issue very urgently.