Failed to bind socket for 2620:1e6:100:1605::4:3333

[walmer-bolfet]

I have installed ckpool. It seems to start ok, then displays

Failed to bind socket for 2620:1e6:100:1605::4:3333
Connector failed to bind to socket, retrying in 5s

This repeats until the app returns:

Connector failed to bind to socket for 2 minutes with errno 99: Cannot assign requested address
Connector failure, shutting down with errno 99: Cannot assign requested address

I can follow a recipe, but I don't yet have one for this error. Any suggestions?

Thanks