It sounds like some of the NS subsystem files did not get restored.  Was it
the system volume set (MPEXL_SYSTEM_VOLUME_SET) that encountered a disk
crash?  If so you would have needed to do an install from a current SLT,
then RESTORE  @[log in to unmask], @[log in to unmask] with the OLDDATE, CREATE, and KEEP
options.

The user community is able to get back on the system because they may be
connecting with hardwire DTC connections.  DTC's do not require the NS3000
subsystem.