logon failed existing session winstation error

I have an admin user using XP remote desktop to connect to
a Windows 2003 SP1 server. He has connected in the past with
no issues and yesterday he suddenly got Logon Connect Failed
"error connecting to existing sessions for JDOE (ID 0)"

No unusual errors in the XP box or server logs, except Security
record Event ID 682 "Session reconnected to winstation" User
name Unknown, Domain Unknown.

As I workaround I created a second account for the user. When I try
from my PC with this second account, I can connect fine. When the
user connects from the original PC, they get the same connection
error.

I haven't been able to reboot the server. Is there any way to
clear this session that does not show up as session?