Forefront Stirling:: Installation Error 26201: failed to create Database EnterpriseSecurity_Dac_DB

Hi,
i want to install Forefront Stirling (Beta) in a VMmachine and i always get
the following error during the installation process:

Error 26201.Error -2147467259: failed to create SQL database:
EnterpriseSecurity_Dac_DB, error detail: unknown error.

I already created this db manually but the error came back everytime i try
to install it again. All other db's are created without any problems and
only this single db cause the problem.
This error come up during the "Installs DAC Server component".

Does anyone know this problem and maybe has a workaround for it?
Thx

Denis