After some days of struggling with a VMware VirtualCenter installation I wanted to share some information on the Error-Message 25003 which the VC-setup gave me while trying to recreate/update the VC-Database. The solution in my environment (VC-2.5.0u3 + Oracle 10.2.0.3 with Oracle Instant Client 10.2.0.4 + Oracle Instant Client ODBC Addon 10.2.0.4) was simple (but very difficult to find ;):
I only got the problem if there was still an active VC connected to my OracleDB while trying to recreate/update the VC-Database. This happened because I tried to reproduce another error. So I still had a VM with VC running while I tried to install a new VC with the same DB in a different VM. Simply shutting down the VM with the old (outdated) VC solved the error.
So in short: if you get the Error 25003 while trying to install VMware VirtualCenter check if there's still another connection to the database in which you try to install VC.
