Lotus Notes

I am using Lotus Notes 5.0.1 and myself and a few colleagues have found that our corporate address book has disappeared. When we try and address a mail to somebody we can only choose from our own personal address books but the main address book of everybody in the company has disappeared. Other colleagues do not have the problem. Our internal Notes support team have not been able to find a solution other than a re-install. Does anyone have any ideas?