This question is definitely answered. I had the identical error and stopping the vmware update manager service as described resolved the issue. I'm not sure how to bring this to Vmware's attention...nothing came up when I searched for the error in the vmware knowledgebase. Thank goodness for Google.
Thought I'd dive in here and help the Google rankings.
Exactly the same issue - after upgrading vCenter 4.1 to U2 and attempted upgrade of the update manger resulted in "Error 25113: Setup Failed to generate JRE SSL Key".
Stopping the update manger services at the point where the installer asks about SQL credentials allowed this to complete without issue.