Mac OS x permission issue with external logins

I have a Mac OSx Tiger Server 10.4.10 with 30 users. Everything is fine and we use LDAP to enter users via workgroup manager. However, when they attach an external drive the permissions ALWAYS are locked to one user so I cannot open a file or copy a file from the external drive.

This does not happen with a flash drive, ony happens with an external drive formatted with HPFS (fat32 works fine).

I tried deleting the user and home directory, still have problem.

If I log into to a local computer account with the network cable pulled, everything is fine.
If I log into the local account with network plugged in, same permission issue.