Add node failed on 181 with exit status 500 after making the rest call

From the test logs
2012-04-03 22:38:33,873 - root - INFO - adding remote node : 10.1.3.75 to this cluster @ : 10.1.3.74
2012-04-03 22:38:33,910 - root - ERROR - http://10.1.3.74:8091/controller/addNode error 400 reason: unknown ["Prepare join failed. Got HTTP status 500 from REST call post to http://10.1.3.75:8091/engageCluster2. Body was: \"\\\"Unexpected server error, request logged.\\\"\""]
2012-04-03 22:38:33,911 - root - ERROR - add_node error : ["Prepare join failed. Got HTTP status 500 from REST call post to http://10.1.3.75:8091/engageCluster2. Body was: \"\\\"Unexpected server error, request logged.\\\"\""]
ERROR

From ns_server logs

2012-04-03 22:37:25.350 ns_memcached:1:info:message(ns_1@127.0.0.1) - Bucket "default" loaded on node 'ns_1@127.0.0.1' in 0 seconds.
2012-04-03 22:37:36.196 menelaus_sup:1:info:web start ok(ns_1@10.1.3.76) - Couchbase Server has started on web port 8091 on node 'ns_1@10.1.3.76'.
2012-04-03 22:37:36.219 ns_cluster:3:info:message(ns_1@10.1.3.76) - Node ns_1@10.1.3.76 joined cluster
2012-04-03 22:37:36.769 ns_cluster:0:info:message(ns_1@127.0.0.1) - Decided to change address to "10.1.3.74"

2012-04-03 22:37:36.783 ns_node_disco:5:warning:node down(nonode@nohost) - Node nonode@nohost saw that node 'ns_1@127.0.0.1' went down.
2012-04-03 22:37:36.785 ns_node_disco:4:info:node up(ns_1@10.1.3.74) - Node 'ns_1@10.1.3.74' saw that node 'ns_1@10.1.3.74' came up.
2012-04-03 22:37:36.910 ns_cluster:0:info:message(ns_1@10.1.3.74) - Renamed node. New name is 'ns_1@10.1.3.74'.

2012-04-03 22:37:37.170 ns_cluster:0:info:message(ns_1@10.1.3.74) - Started node add transaction by adding node 'ns_1@10.1.3.76' to nodes_wanted

2012-04-03 22:37:37.341 ns_memcached:1:info:message(ns_1@10.1.3.76) - Bucket "default" loaded on node 'ns_1@10.1.3.76' in 0 seconds.
2012-04-03 22:37:37.787 ns_node_disco:4:info:node up(ns_1@10.1.3.74) - Node 'ns_1@10.1.3.74' saw that node 'ns_1@10.1.3.76' came up.
2012-04-03 22:37:37.868 ns_cluster:5:info:message(ns_1@10.1.3.74) - Failed to add node 10.1.3.75:8091 to cluster. Prepare join failed. Got HTTP status 500 from REST call post to http://10.1.3.75:8091/engageCluster2. Body was: "[\"Unexpected server error, request logged.\"]"