Hello,
I have now a similar problem I think.
I am running Arc SDE x64 Postinstallation for SQL Server on MS Server 2008 (x64).
When I enter all information and click "next" a messagebox appears saying: "the geodatabase has been sucessfully created".
When I click "ok" the box disappears and the error from this thread appears. After I click on "ok" the error also disappears and the installation dialog is going next. I now am at the dialog to specify the ArcSDE configuration files.
When I go back, and retype the (same) geodatabase name (it is the only field which is blank now) and klick on "next" only the native error occurs but every time with a different error number (its often 334xxxx).
The directory of the data file and log file was on another drive than "C:\" so theres no windows OS-deny.
Well I could go further now, but how can I be sure, that all works fine?
Thanks for help and advice.