Machine names v. User names

Good Morning...

Unfortunately one of our mainframe processes require a
local machine name that is identical to the local user
account name. For example machine name PCB must have a
user for FTP access that is also PCB. XP doesn't allow
that and provides the error message, "Local Users and
Groups: The user name may not be the same as the computer
name PCB." I've search the policies and found nothing to
disable this feature. Is there a registry setting that I
can allow this to be done?

Thanks in advance for any help you can provide...

Pete