[Andrew Thompson]

Thanks, Curt. This gets more and more interesting and bizarre.

I did as you suggested and reverted to a back-up from the day before yesterday - but the result is the same: a whole bunch of actions which had been completed, modified or rescheduled have reappeared in their original form, plus a whole bunch of new actions added in the last few days have disappeared.

I've manually restored the status of the actions etc and have set the prefs to backup more frequently.

Support suggested I may have had iDisk synch turned on and that this may have caused the problem, but I didn't have it on.

Curiouser and curiouser ... but thanks for the great help.