How-to: resolve hbase "org.apache.hadoop.hbase.TableExistsException: hbase:namespace"

Error:

2015-06-24 13:34:05,251 FATAL [master:60000.activeMasterManager] master.HMaster: Failed to become active master
org.apache.hadoop.hbase.TableExistsException: hbase:namespace
        at org.apache.hadoop.hbase.master.handler.CreateTableHandler.checkAndSetEnablingTable(CreateTableHandler.java:152)
        at org.apache.hadoop.hbase.master.handler.CreateTableHandler.prepare(CreateTableHandler.java:125)
        at org.apache.hadoop.hbase.master.TableNamespaceManager.createNamespaceTable(TableNamespaceManager.java:233)
        at org.apache.hadoop.hbase.master.TableNamespaceManager.start(TableNamespaceManager.java:86)
        at org.apache.hadoop.hbase.master.HMaster.initNamespace(HMaster.java:897)
        at org.apache.hadoop.hbase.master.HMaster.finishActiveMasterInitialization(HMaster.java:739)
        at org.apache.hadoop.hbase.master.HMaster.access$500(HMaster.java:169)
        at org.apache.hadoop.hbase.master.HMaster$1.run(HMaster.java:1479)
        at java.lang.Thread.run(Thread.java:745)
2015-06-24 13:34:05,255 FATAL [master:60000.activeMasterManager] master.HMaster: Master server abort: loaded coprocessors are: []
2015-06-24 13:34:05,256 FATAL [master:60000.activeMasterManager] master.HMaster: Unhandled exception. Starting shutdown.
org.apache.hadoop.hbase.TableExistsException: hbase:namespace
        at org.apache.hadoop.hbase.master.handler.CreateTableHandler.checkAndSetEnablingTable(CreateTableHandler.java:152)
        at org.apache.hadoop.hbase.master.handler.CreateTableHandler.prepare(CreateTableHandler.java:125)
        at org.apache.hadoop.hbase.master.TableNamespaceManager.createNamespaceTable(TableNamespaceManager.java:233)
        at org.apache.hadoop.hbase.master.TableNamespaceManager.start(TableNamespaceManager.java:86)
        at org.apache.hadoop.hbase.master.HMaster.initNamespace(HMaster.java:897)
        at org.apache.hadoop.hbase.master.HMaster.finishActiveMasterInitialization(HMaster.java:739)
        at org.apache.hadoop.hbase.master.HMaster.access$500(HMaster.java:169)
        at org.apache.hadoop.hbase.master.HMaster$1.run(HMaster.java:1479)
        at java.lang.Thread.run(Thread.java:745)
2015-06-24 13:34:05,256 INFO  [master:60000.activeMasterManager] regionserver.HRegionServer: STOPPED: Unhandled exception. Starting shutdown.

Resolve:

Remove /hbase in zookeeper and restart hbase.

-  Go into zookeeper lient via:  hbase zkcli

-  rmr /hbase

-  start hbase: hbase-start.sh