After changing the vCenter IP Address, I ran into a a couple of issues with VUM. Which generated the following error messages:
Plug-In Manager Plug-in is unavailable for the following server(s): – VMF-VC01.vmfocus.local
vSphere Client There was an error connecting to VMware vSphere Update Manager – [vmf-vc01:443]. The request failed because of a connection failure. (Unable to connect to the remote server).
Steps Taken To Resolve – DNS
The first step was to double check my DNS, I had already performed the tasks below after changing vCenter IP Address.
- Removed reverse DNS zone for old vCenter subnet and added new reverse DNS zone for correct subnet
- Updated DNS for ESXi Hosts & vCenter
- Cleared DNS Cache on vCenter and Domain Controller
Steps Taken To Resolve – VMware KB
The next step was to make any amendments to VUM. This consisted of the following:
- Checked DSN to VUM database continued to work
- Stopped vSphere Update manager Service
- Followed the instructions under VMwareKB101322
Both of the original errors continued to persist, so the next step was to follow a KB for vSphere 4.1
- Stopped vSphere Update manager Service
- Followed the instructions under VMwareKB1014639
Again this did not resolve the issue, however it did mention a vCenter Update Manager Utility.
Resolution
Lunch VMwareUpdateManagerUtility.exe which is located in C:Program Files (x86)VMwareInfrastructureUpdate Manager
Connect to vCenter using the correct IP Address
Select Re-register to vCenter Server and enter the new IP Address of vCenter and your credentials. Click Apply
Once complete, re-enable the VMware vSphere Update Manager Plug-In and you should receive the trusted Security Warning dialogue box. Which means vCenter and VUM can talk, everyone’s a winner!
VMFocus 
Funny you mention it, I ran into the same issue last week. Good post dude!
On 5.5, the KB did not help me either. Very Nice post!
Just had this problem and the fix here worked like a charm!
Thank you
This is the only solution that worked. Thank you!
Thank you