NW 6.5 sp3, Novell Cluster 1.7.1, Clients are XP with AutoCAD Building

Using ABS a user has locked a file on a clustervolume.
Later he has to delete the file, but are not allowed ,since it is still
locked. The software is stopped, the user has logged out and the file is
still locked. In Netware Console is tell us that it is locked by connection
168. But in Connection there is no connection 168.
I guess that we could solve it by moving the volume to an other server in
cluster, but this some will loose there connection to the volume, so this is
not an option at daytime.
How can we prevent this to happen? Is there a patch that solves this issue?
Is there an other way to unlock the locked files?

Regards and thanks