error attempting to delete event

I get this error:
"The calendar http://server.fsm.private/zulu/calendars/fsm/ could not be accessed. It may be in use by someone else. Try again later.
GO OFFLINE or REVERT TO SERVER are offered as buttons in the dialog"
When I delete an event from filemaker, and then attempt to delete the same event from iCal. I also get the error if I attempt to change the event in iCal
Also, note that when I delete the event in filemaker, and then refresh the calendar, the event does not get deleted in iCal.
Thanks for the help!
Darren Burgess
"The calendar http://server.fsm.private/zulu/calendars/fsm/ could not be accessed. It may be in use by someone else. Try again later.
GO OFFLINE or REVERT TO SERVER are offered as buttons in the dialog"
When I delete an event from filemaker, and then attempt to delete the same event from iCal. I also get the error if I attempt to change the event in iCal
Also, note that when I delete the event in filemaker, and then refresh the calendar, the event does not get deleted in iCal.
Thanks for the help!
Darren Burgess