Windows Server 2003 allows you to use the Limit profile size Group Policy Object at User Configuration / Administrative Templates / System / User Profiles to limit the size of roaming profiles.
If you enable this policy, the Profile Storage Space dialog is displayed when a user logs off if their profile exceeds the maximum size. When this occurs, they are required to reduce their profile size before they can log off.
A user can bypass this limit and successfully log off if they press ALT + F4 two times.
To prevent this behavior, install the latest service pack for Windows Server 2003.