The usual signs are "requested boost pressure" being a lot higher than standard, and there's a "Flash count" counter which shows 0 on a standard car. 1 or more indicates a map has been uploaded.
From your description it sounds more like an under-boost condition. The usual suspect for that is a split diverter valve. Most folk upgrade to the GFB DV+, or a revision D or G VW part if you don't fancy dabbling with aftermarket bits.
What is the exact error that's putting the money light on?