String cannot be of zero length error when trying to use Form Event Wizard for AfterFieldChange event

Hello I get the following error when attempting to use the form event wizard to try and show a message box when a field has changed. I am trying to do something a bit more complex than the message box but since I cant get the message box test to work correctly I don’t want to try adding anything else.

Has anyone encountered this error before and does anyone have any info on what it is actually saying?

Turns out the person who initially created this customization deleted some of the comments the wizard uses to figure out where to insert its information.