XDCR Connection Closed 4.0.0

Hi we are trying to set up XDCR between two couchbase XDCR clusters. I am able to set up it up from A->B but when I try to set up the replication back from B->A I get :

<CLUSTER B>:Error constructing vb couchApiBase map for bucket versions on remote cluster <CLUSTER A> because of failure to retrieve bucket info err = Get http://<CLUSTER A>t:8091/pools/default/buckets/versions?bucket_uuid=7c01cebd2c85dcb6dc391676b62263dc: read tcp <CLUSTER A IP>:8091: use of closed network connection

It seems to be stuck at the stage Source nozzles are wired to target nozzles
(I dont know if there are progress stages beyond that.)
Im thinking that there may be some firewall issue, that is blocking xrdc, and causing a connection timeout, but who knows. Anyone have any ideas on what to check ?

The relevant log entry in goxdcr.log seems to be

Replication Status = mapÆfa109c8a5f104eb84eaba29588214ee9/versions/versions:name=æfa109c8a5f104eb84eaba29588214ee9/versions/versionså, status=æPendingå, errors=æÆæ"time":"2016-11-30T02:15:49.32644522Z","errMsg":"Error constructing vb couchApiBase map for bucket versions on remote cluster minke-a1-whale.co1.qprod.net because of failure to retrieve bucket infoØnØn err = Get <CLUSTER A>:8091/pools/default/buckets/versions?bucket_uuid=7c01cebd2c85dcb6dc391676b62263dc: read tcp <CLUSTER A IP>:8091: use of closed network connection"å,æ"time":"2016-11-30T02:12:48.56445776Z","errMsg":"Error constructing vb couchApiBase map for bucket versions on remote cluster minke-a1-whale.co1.qprod.net because of failure to retrieve bucket infoØnØn err = Get <CLUSTER A>t:8091/pools/default/buckets/versions?bucket_uuid=7c01cebd2c85dcb6dc391676b62263dc: read tcp <CLUSTER A IP>:8091: use of closed network connection"å,æ"time":"2016-11-30T02:09:47.800415075Z","errMsg":"Error constructing vb couchApiBase map for bucket versions on remote cluster minke-a1-whale.co1.qprod.net because of failure to retrieve bucket infoØnØn err = Get http://<CLUSTER A>:8091/pools/default/buckets/versions?bucket_uuid=7c01cebd2c85dcb6dc391676b62263dc: read tcp <CLUSTER A IP>:8091: use of closed network connection"å,æ"time":"2016-11-30T02:06:37.00033383Z","errMsg":"Error constructing vb couchApiBase map for bucket versions on remote <CLUSTER A>t because of failure to retrieve bucket infoØnØn err = Get <CLUSTER A>:8091/pools/default/buckets/versions?bucket_uuid=7c01cebd2c85dcb6dc391676b62263dc: read tcp <CLUSTER A IP>:8091: use of closed network connection"åÅå, progress=æSource nozzles are wired to target nozzle