NetWare Error -631 when installing the NDS

This was something I encountered with Novell NetWare 6.0 SP5e, so it's only interesting to a small group, but I thought I'd write about it as when I had the problem I didn't find anything on the web about it. Here goes:

Scenario
Two servers installed with NetWare 6.0 SP5e. Let's call them servers A and B. 
Server A had the master replica (NDS/eDirectory).
Server B had a read/write replica.

I wanted to add a third server into the tree, to put a replica on it. This third server we'll call Server C.

On server C, I entered NWCONFIG, select Install Directory Services onto this server. After entering the tree and IP address of server A (where the Master replica is located) I received the following error:

An internal error has occurred. DSI cannot add a partition replica. Error description: unknown error -631 (fffffd89 hex) - (DSI-5.0032)

What I tried...
I tried all kinds of things, ensuring the time was correct on all the servers, running DSREPAIR (all servers showed zero errors). I checked the http://support.novell.com website and Google, but no, I couldn't find anything applicable to my situation.


My solution
My solution is probably more of a workaround if I'm honest. I didn't get to the bottom of this problem, but I got it to work - here's what I did:
I designated Server B as Master. From Server C I ran NWCONFIG, Install Directory Services onto this computer, I entered the IP address of Server B (now set as Master). 
It worked!!! No -631 error!

In a nutshell, if you have -631, just try installing the NDS/eDirectory from another server.


Why?
I don't know. I ran DSREPAIR and had zero errors so I really don't understand why I couldn't install the NDS replica onto Server C from Server A. After the installation worked, I designated Server A as the Master again, it was and is still working fine. It's a mystery!