First thing I tried was deleting preferences, but that didn't work. So I just simply reinstalled 10.2.6 combo updater and everything was back to normal.
[robg adds: Apple has a Knowledge Base article about this problem, but it's a bit older and refers to 10.2.2 as fixing the issue. This is the first I've heard of the problem in 10.2.6, but if you've had a similar problem, please share your experience (and the fix!).]

