Office 2000 continuously asks user

We have a hybrid NT4.0 and Win2k domain.
Lately several (5-10) users have lost the ability to open Word/Excel/Access Office 2000.
If you look at the shortcut it states “Application (installs on first run)”. We must log in again as ‘admin’, run the install, then the user can again use the apps. This occurred all of a sudden on pcs located in different areas of the company (same building). Could this be a license issue?virus?