I think saying 1 error is too many is a little extreme. I've had one or two instances where I've seen 1 error in a few hours of running the test. That's not out of the question. Errors don't happen often in good RAM, but they do happen occasionally. Every time I've come across a stick of bad RAM, it has had hundreds of errors at the very least in memtest...

I think anything up to say, 1 or 2 errors in an hour long test is acceptable. Especially if it shows up in one run, but you re-run the test again later and it doesn't show up.