Information store could not be opened error - delegate

[olivia]

Hi,

One of our staff is experiencing the error "information
store could not be opened" when trying to make
appointments for her supervisors.

I've asked those concerned to check that she is set as
editor for calendar and tasks and also that "delegate
receives copies of meeting-related messages sent to me"
is ticked.

Apart from that the only other thing I can think of is
for her to be deleted as a delegate and re-added, I read
somewhere that permission can be reset?

Thanks,
Olivia