I am also having the same setup(two indexes) and my listening port is 51099 and facing same issue. futher I can see below error message as well in forwader log
12-22-2012 22:54:53.703 +0000 INFO TcpOutputProc - tcpout group splunk_recieving_nodes using Auto load balanced forwarding
12-22-2012 22:54:53.703 +0000 INFO TcpOutputProc - Group splunk_recieving_nodes initialized with maxQueueSize=512000 in bytes.
12-22-2012 22:54:53.703 +0000 ERROR TcpOutputProc - the 'defaultGroup' property contains an invalid group name - splunk_recieving_nodes - skipping
12-22-2012 22:54:53.703 +0000 WARN TcpOutputProc - Default groupList has not yet been calculated!