Node reconnecting (no replies)

Hello

Since last few months i have problem with random reconnecting nodes in cluster.
Does anyone know how to resolve this problem or how to debug it ?

2011-01-24 15:16:51 [MgmtSrvr] ALERT -- Node 2: Node 6 Disconnected
2011-01-24 15:16:51 [MgmtSrvr] INFO -- Node 2: Communication to Node 6 closed
2011-01-24 15:16:51 [MgmtSrvr] INFO -- Node 3: Communication to Node 6 closed
2011-01-24 15:16:51 [MgmtSrvr] ALERT -- Node 3: Node 6 Disconnected
2011-01-24 15:16:54 [MgmtSrvr] INFO -- Node 3: Communication to Node 6 opened
2011-01-24 15:16:54 [MgmtSrvr] INFO -- Node 3: Node 6 Connected
2011-01-24 15:16:54 [MgmtSrvr] INFO -- Node 3: Node 6: API mysql-5.1.51 ndb-7.1.9
2011-01-24 15:16:54 [MgmtSrvr] INFO -- Node 2: Communication to Node 6 opened
2011-01-24 15:16:54 [MgmtSrvr] INFO -- Node 2: Node 6 Connected
2011-01-24 15:16:54 [MgmtSrvr] INFO -- Node 2: Node 6: API mysql-5.1.51 ndb-7.1.9


Thanks