Unknown Error on beforeSubmit xedit

Hi folks;

I'm getting an "unknown error" being thrown to the client window while testing a beforeSubmit script on a mass update and I cannot figure it out.  It's possible that it's not even my script that's throwing the error (in fact, I have a try/catch on the whole thing and nothing is getting caught) but it's pretty clear that it's the introduction of my script that's causing the error.

What my script does is pretty simple - it loads the current record if it's an xedit and pulls a few data fields.  I have some basic logic (if A=X and B=Y type stuff) and if it's all true then I set some fields and email the customer a welcome email.