NSS Free Tree block xxx is corrupt on pool “SYS”

Ever seen that dreadful error message while your NetWare 6.5 server is trying to activate the SYS pool? I have, and I won.

First you need to prevent NetWare from activating any NSS pools during boot. Shortly after server.exe is running you are given the option to abort the launch altogether. Do so. Next, in the C:\NWSERVER directory, create a text file called nssstart.cfg. Insert the following line:

/poolAutoDeactivate=all

Save the file and exit the editor. Next you need to engage server.exe with the following command:

server -ns

This will start NetWare but without running any of the commands in startup.ncf nor autoexec.ncf.  Type the following commands when the System Console becomes available:

startup.ncf
loadstage 1
nss /PoolRebuild=SYS

Once the nss command has completed, exit to DR-DOS by using the down command. Rename the file nssstart.cfg to something you can easily remember, say nssstart.cf_. Reengage server.exe as you normally would and keep your fingers crossed. I prefer to start server.exe with -nl for no logo.

TID 10077587 and this thread pointed my in the right direction.