I Added this code:

Set Field_Error Field tTestBatch.Production_Lot to 404 "You MUST select a Production lot from the popup list."

to a field with a ValidationTable set for validation.

When Testing I got:

Click image for larger version. 

Name:	errFail.png 
Views:	41 
Size:	54.4 KB 
ID:	13301

Why does this pop up as an "unhandled error" when by definition, adding a specific error message handles the error. I'd expect a userError at this point.