I had the same issue.
The problem for me turned out to be that the hbase.zookeeper.quorum was not set in hbase-site.xml in the server that submitted the mapreduce job. Ironically, this is also the same server that was running hbase master. This defaulted to 127.0.0.1 which was where the tasktrackers where trying to initiate the connection from. The fact that the zookeeper quorum was not set in the tasktrackers was useless.
