Actually it was a different bone-headed error. I had started the install, had to put it on hold for a few months, and then before resuming updated from cvs again. As a result, my database.conf file was from a previous version of WeBWorK, with enough differences from the new version to really mess things up. For some reason I had thought to update global.conf, but didn't even think about database.conf (which I rarely have to touch anyway.)
Seems to be working now.