Diary Page In Use
Applies to old style diary only
This indicates that another user is making an appointment in this diary for the same date as you. The message will show you the user ID and location of the terminal.
If you are 100% sure that user is not on the system then you can get past the lock by entering an * at the 'Page In Use' prompt.
Please only use this option if you are sure that it is a rogue lock.