The first step is to make sure that it is not a credentials issue.
1- Open the vmware configuration (if you can). Highlight 'IP', right-click and select, 'Edit'.?
2- Press the Test button (the patrol / password credentials should already be populated). Can you successfully 'Test' your connection??
3- If this fails, then log into vCenter directly with the 'admin' account, and verify that your connection string in the probe is set correctly.
If it is not a credentials issue, the next step is locate the java.security file from the \lib\security and comment out the following:
"jdk.certpath.disabledAlgorithms=MD2, RSA keySize < 1024"
It is usually found on the following path "C:\Program Files (x86)\Nimsoft\jre\jre7\lib\security"
After making the change restart the robot.