** Can anyone give me a hint as to what I might be doing wrong? **
I don't think you're doing anything wrong, it has to be something with file or directory permissions on the server.
You could try renaming or deleting (after making a backup of) the plugins.txt file located in the calendarscript/plugins directory and seeing if it gets recreated properly. If it does, you'll have to turn on all the plug-ins again.
This advice is untested so use at your own risk!
Dan O.
[This message has been edited by DanO (edited August 06, 2003).]