Loosing windows profiles

We are having trouble with windows profiles in a Netware/Zenworks environment. We have them set up in Zenworks to store in the user area, and to download to the \winnt\profiles directory when users log in. Any changes that take place during the session get uploaded again when the user logs out.
It worked fine for months, but for no apparent reason, it started to fail. Now users loose their profiles (with their mail and other preferences) almost every day. There is no pattern: different users, different days, different locations… but not consistently. A user might loose his profile today, keep it tomorrow, loose it again the next day…
This is driving us crazy. Please HELP!
Thanks