Then it could be that Update Manager PowerCLI has a problem with PowerCLI 5.1 R2.
In the Release Notes it does only mention PowerCLI 5.1, and not PowerCLI 5.1 R2.
Is downgrading PowerCLI an option ?
A nuissance, I know.
It seems the Update Manager PowerCLI version didn't keep up with the PowerCLI version.