SCOM agent error Microsoft ESENT Keys are required

Ran into this error while manually changing some SCOM agents. They actually needed both an update and a second management group configured.
While trying to update the settings of the SCOM agent through Add/Remove programs on Windows 2008 boxes I got the error “Microsoft ESENT Keys are required” and it did not change anything.
So what happens is that User Account Control (UAC) could not differentiate between an admin account and a non admin account in this case and did not give an UAC prompt. You can read about it in this KB:
The workaround is the following:
Open an Elevated command prompt and run one of the following commands, depending on the SCOM version.
System Center Operations Manager 2007 SP1:
msiexec /I{768DB8BD-CB3A-43F4-9A4C-BA2921D27AD3}
System Center Operations Manager 2007 R2:
msiexec /I{25097770-2B1F-49F6-AB9D-1C708B96262A}
In my case this worked.
After this I found a post by Mark Wolzak pointing to the same, but also pointing out that in some cases the GUID might have changed and how to find the GUID needed in the command. In that case you would see an error “This action is only valid for products that are currently installed.”
To get around that you will have to find the GUID in the registry somewhere in this path: ‘HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall’ and search for the DisplayName that starts with “System Center Operations Manager 2007” and find the command you need in the ModifyPath value.
Good Luck!
Bob Cornelissen