The following information is from MS KB 307853:
? You cannot use offline files.
This can occur if the Fast User Switching feature is enabled. You cannot use fast user switching when you use offline files. To disable the Fast User Switching feature: 1. Click Start, and then click Control Panel.
2. In Category view, click User Accounts.
3. Click Change the way users log on or off.
4. Clear the Use Fast User Switching check box, and then click Apply Options.
5. Quit User Accounts, and then quit Control Panel.
Does this help?