A quick note to hopefully publicize a problem I had which I see is discussed in the VMware Community Forums already.
After building a new vCenter Server and Upgrading the vSphere 4.0 databases for vCenter and Update Manager. I noticed I could not scan hosts that were upgraded to 4.1. To be fair, by upgrading I mean rebuilt with a fresh install but with the exact same name and IP addresses. Seems that the process I took to upgrade has some kind of weird effect in the Update Manager Database. The scans fail almost immediately. I searched around the internet and found a couple of posts on the VMware Forums about the subject. One person was able to fix the problem by removing Update Manager and when reinstalling selecting the option to install a new database. I figured I didn’t have anything important in my UM database so I gave it a try and it worked like a champ.
Right now there is not any new patches for vSphere 4.1 but I have some Extension packages that need to be installed (Xsigo HCA Drivers). I wanted to note that I like the ability to upload extensions directly into Update Manager. This is a much cleaner process than loading the patches via the vMA for tracking and change control purposes.
I had similar issues with VUM 4.1 and its database. I ended up blowing the database away, reinstalling VUM from scratch and creating a brand new DB. Afterwards, everything worked perfectly.