Cannot connect to the vCenter Operations server. Check your network connection, and the running state of the virtual machines in the vCenter Operations Manager vApp
I check the vApp and network connectivity and everything was fine. There is no firewall in-between these two hosts so I knew that wasn't the issue. I then tried unregistering and re-registering the vCenter servers in vCenter Operations Manager by logging into the vCenter Operations Manager admin interface and un-registering and re-registering both vCenter Servers:
Once completed the vCenter Operations Appliance showed that it was unlicensed so I had to go back to vCenter and correctly license the solution again. After a few minutes the appliance was fully licensed but still no information in the Health State. My other vCenter which was not upgraded to 5.5 U2 works fine so I can only assume the upgrade done something with the certificates.
If anyone knows the fix for this then let me know, otherwise I'll update this post when I fix it
** UPDATE - 11/09/2014 **
I've just noticed that the option to open an object within vCenter Operations is greyed out on the vCenter that was upgraded to 5.5 U2 but not on the vCenter that's still 5.5 U1
vCenter 5.5 U1
vCenter 5.5 U2
I've also check the vCenter Managed Object Browser and both vCenter servers look to be configured identical for com.vmware.vcops so that rules out certificates.