Here a small post that hopefully will help some people in the future that are stuck with the same issues. I am still missing some info, but I discovered the workaround for the following "symptoms".

FACT’s

I have a VMware environment in which I can play with Oracle BAM and OEM Grid Control on Windows 2003. My current OEM Grid is 10.2.0.3. Because 10.2.0.4 is already out for a while I decided to upgrade my current 10.2.0.3 release. I checked and verified all prerequisites needed before the upgrade. Because I once upgraded the OEM from 10.2.0.1 to 10.2.0.3; and my initial install at that time was an "out of the box" install, no extra steps needed to be done before I could start with the upgrade to 10.2.0.4.

Now it comes… (more…)