did you by chance upgrade to php 5.3 and above? i'd recommend not using anything newer than 5.2.12 for compatibility reasons.. this causes drupal headaches too (unless they've fixed that)
Interesting. I'm running 5.3.1 on five servers and 11 drupal installations (all version 6.15) without a problem. Same with multiple WordPress installs. Got just one UBB and it has decided to start flaking.
