I am not sure if your U drive mapping will work especially if you are using standard shares generated by the user manager. For Win98 every user must be assigned a share. The user manager creates pseudo shares only mapable by NT or higher.

We run Win98 clients & the only time we have lock outs is if we get password problems with one of the students. It seems to me for lock out to happen implies that the server is responding to an error condition it is sensing, it is not the client system responding. Are you checking the server log to see why the server is locking out the user or machine?

As to random mapping of drives my thoughts are:

1) You may not have a compatible 4.10 version of kxrpc running on all PDC & BDC.
2) You may not have replication running on all PDC & BDC
3) Some of your systems may have old versions of kixtart DLLs on them.
4) Are you calling kixtart from a BAT file? You should.
5) Look at the kixtart log file on the problem client machines. Are you getting any error messages?
6) Try visiting MCA's site (you can get there but choosing "scripts" on the main page of this board. Try out is kixstrip & kixcheck utilities.
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Jack