Collapsiblock quits working and breaks js in whole site

I am running Drupal 6.1. The site has been running with a custom theme built on Framework and with Collapsiblock working for months. Then all of a sudden the whole site was broken. None of the javascript was working.

When we changed to a different theme, everything would work (I tried Minelli). But after a few weeks of running in the new theme, it stopped working too.

Finally, we found that everything would work again if we disabled Collapsiblock.

I have tried removing Collapsiblock and JSTools, then reinstalling them. This did not fix it.

Any ideas on what the problem is would be really, really appreciated.