volgens Mike Sangray.
I worked around this issue by doing a git install of 2.5, copying back my config.php file, and manually downloading/installing new plugins. Not sure if it's a bug, or just a bad procedure on my part regarding plugin code upgrades.
Also, I'm having an issue with the new attendance module - I'll create a new post for that one. Here's a preview "DDL sql execution error""Table 'mdl_attendance' already exists"
Mike