Vista - Offline Files Lock Domain Account on Vista

I run with the following configuration:

Vista laptop in workgroup mode.
I use local user account on that laptop.

I connect to network drive using domain user identity and it works well if
Offline Files are disabled.

Most of my directories on a network drive are set for offline
synchronization. Yesterday I enabled offline files and it worked well until
today.

Today I powered on my computer, logged in as a local user and was able to
browse network drive without a problem. A few minutes later my domain
account got locked out.

I had no choice, but to disable Offline Files, reboot, call IT support to
unlock my account. And so far account is fine.

How do I make Offline Files to work without locking my domain account?

Thank you