the only safe bet is that the stu spacing probably won't be consistant...did the stud sensor you were using have a deepscan mode on it...if not try one that does....i have had pretty good luck with those in the past with plaster walls...

Thanks for the reply. Yes, it had deepscan and I tried it. It did seem to find one stud, but it was the only one indicated in a 9' long wall (there were some other blips, but nothing as good as the one) and the one it did find was about 2.5' off of one edge...