Network communication between two nodes in a Hadoop cluster

I am running a 7 node hadoop cluster with each box running Ubuntu 12.04. It is running CDH4 setup using Cloudera Manager. It was already setup and running when I came in but now I'm running into a communication issue between the master and slave1.

The manager GUI says that it cannot communicate with slave1. SSH and Ping to this node from the master fails. However, SSH and PING from all other nodes in the cluster works absolutely fine. I have also verified that the default gateway for all the nodes in the cluster is the same.

I believe it is an issue with the SSH keys between master and slave1 but not sure how exactly to fix it. Would appreciate your help and suggestions.