The thing is, they've still taken the time to actually write "I get an error". So by principle of reciprocity, you can just take 2 seconds to say, "What's the error?" Usually that won't lead anywhere; but as long as you don't spend more time than they are, you aren't really wasting much time; and they can't exactly complain that you weren't helpful. And occasionally it will lead somewhere, in which case it's a win.