hi Philipp,
You can try the following. Follow the instructions in the Virtual Appliance installation guide, section "Configuring Serial Console for the VM", but don't send the console output to telnet, choose "file" and save it somewhere in your datastore that makes sense. I'd recommend saving it in the same datastore folder as the VMM itself.
Then, boot it up, wait for it to error out etc, and then collect the log file above plus the "vmware.log" from the VMM datastore directory. Between these two files the problem should become clearer.
Post them here for a first glance, or, raise a TAC ticket if the problem is not obvious.
hth
-jeff