Maybe they accidentally closed their personal address book. We had a couple of people here who hated the Frequently Used one so when they went to close it, they accidentally closed their personal one.
On a website I saw, someone wrote they reinstalled wms.exe and then reinstalled GroupWise and then went into the blank address book. Then go to File and Services and click Add and simply add Novell GW Address Book and Personal Address Book. Close out and open GW again in order to see it.
I read someone else had the same problem after installing Office 2000. After removing Office 2000 and a new install without Outlook 2000, no more problems.
Hope that might help.