In reply to

ej - two things.

First, it doesn't appear you're raising an error anywhere, which, I believe is part of why it's not doing anything. Even if it does catch a MerchantID with a length > 4 - it will just return a message, and not really stop execution, no?

second, what is the error message you get on the hidden parameter?

You are correct, the report runs as normal however I'm not sure where the message is being returned. I expected it to be in my hidden parameter but when I make it unhidden and run the report it's just empty space. The error message I was hopping to see is the msg returned by the function, the "Merchant ID should not exceed 4 characters" (or something like that).

Suggestions? I originally got this idea from posting http://www.sqlservercentral.com/Forums/Topic537763-145-1.aspx#bm537914