Did you add the mass storage drivers to the ‘mass storage drivers’ section of the system package? It’s in the ‘computer settings’ I believe.
To complete this - the main error was a wrong harddisk-driver... Following is the used solution:
1. "Computer Settings"-tab => "Mass storage drivers":
"LSI MegaRAID SAS RAID controller Driver (Serer 2003 32-bit)", msas2k3
2. "Unattend Entries"-tab (lower part for additional entries):
"LSI MegaRAID SAS RAID controller Driver (Serer 2003 32-bit)" =OEM
Both parts had to be filled to get this working. Fill in only the "1."-field even was not reflected in the upper part of the "Unattend Entries"-tab.