deleting of caldav accounts impossible

Hi,

in my office runs a 10.6.Server with iCal-service enabled. There several clients connected. After having set up the server from scratch with new user accunts etc. some clients are still trying to coonect to old calebder accounts that don´t exist anymore. i get an error message.

If I delete these accounts they immediately appear again or at least with the next start of ical. iCal creates the dead accounts everytime new so that they ar added unlimited. The whole thing is solved if I create a new user, but this would be a lot of work for 15 Clients.