Oulook not updating new email.. 'this folder was last updated at 12:30 pm' message

catalyst

we have a windows sbs 2008 server running exchange server 2007 and about 30 clients connecting to the DC.
all the clients are xp pro using office 2007, and using exchange as their email mailbox setup.
the problem i have is that one of the clients is not updating the mailbox in outlook.
usually you would get 'all folders are up to date' at the bottom of outlook,when it says this you can guarantee that emails will flow in automatically to the users inbox.i have tested this by sending emails from my hotmail account and also set the pc to automatically send&recieve every 1 minute.
but after a while the 'all folders are up to date' message will turn to 'this folder was last updated at 12.30pm' (time differs obvoiusly). once this message appears the messages will stop flowing in automatically and even if you click on send/recieve nothing comes into the inbox,the only way to resolve this is by coming out of outlook and going back in which is an absolute pain.
i have set the auto send&recieve to 1 minute and also played around with the cached mode but still this problem occurs.
any help is appreciated