I've built a 10 node cluster, no problems. However I was adding node 11
and during the process one of the original servers failed - abended (by
cluster services I believe).

Now when I bring either of those two nodes up (the new one or the failed
one) I get the error:

The cluster has lost communication with node (existing node).
(the server attempts to poison pill the failed one - even if its itself)
Node appears to be dead while holding its lock.

It therefore can't poison pill the server and can't be cleaned out.

I've searched the support site but haven't found anything. Any help
would be appreciated.