I'm using vCenter 4.1, running on Windows Server 2008 R2 (x64). Everything is running fine, both vCenter and the Update Manager are up and running and can succesfully talk to their databases (SQL Server 2008 R2 running on the same machine); DSNs are ok.
The server is behind a NAT router, but it doesn't do any traffic control; all outbound ports are open. Web browsing works, and the VMware website can be accessed; no proxy is in use or required.
The problem: everytime vCenter Update Manager tries to download patch definitions, it fails. I've configured it to download ESX 4 and ESX 3 patches, but both task fails. The download URLs were preconfigured in UM, and they are as follows:
https://hostupdate.vmware.com/software/VUM/PRODUCTION/index.xml
https://www.vmware.com/PatchManagementSystem/patchmanagement
Both URLs work when typed in a web browser on the server.
The only error I get is a laconic "Could not download host patch packages" in the vCenter events; no further details are given. This has been going on for more than a month, so I think I can safely exclude some transient problem on VMware update repositories.
Any help is really appreciated.