it seems i managed to fix the issue with My problem, i list down the steps here feel free to try it at your own risk. I am on Mac Platform (10.8.2 Macmini Server)
01. I installed FileMaker Server Advanced 12 (fms_18.104.22.168)
02. When its ask to deploy it do not start deploy the server
03. Download the update from http://help.filemaker.com/app/answers/detail/a_id/11044 (only update) then install it , this may be gives you notification that this application canot run while Filemaker Server open. If you get that error message open the Terminal application (under utilities) and type
fmsadmin stop server
04. Then you will be able to install the update.
05. When you finish the update you can start deploy FM server. my version didn't gave me any trouble at this point and it worked smoothly.
06. When you finish deploy FM server you can also install 22.214.171.1247 update, that will also fix minor bugs of FM server 12
Hope that helps :)
The problem was that the user name on the iMac was set to FMServer and it just so happens that the user name that Filemaker Server tries to create is FMServer. Wow, what dumb luck.
Just changing the user name is not enough, I had to change the name of the Home folder to something else besides FMServer and then it installed without any problems.
Tech Support was able to resolve this for me, but as I stated, none of the documentation mentions this nor does the installation guide.