Recurring Password requests

We have a client who is a press agency - they use shared calendars on Outlook
2007 to log interviews etc for about 6 reporters.

Most users are ok... but two have the same problem, every time they open
Outlook they are asked for the username and password to allow them to view
their colleagues calendars, they have ticked the "remember" boxes but this
does not seem to have any affect.

Any idea's would be gratefully received..

Thanks

Keith