I had also this problem but the solution was not so easy as described above – always got the error.
Solution required for my machine the following steps:
2.)Delete the postgres user if it still exists :
net user postgres /delete
3.) Create the postgres user with a password you can remember:
net user /add postgres <password>
4.) Add the postgres user to the Administrators group:
net localgroup administrators postgres /add
5.) Add the postgres user to the Power Users group
net localgroup "power users" postgres /add
6.) Run a command window as the postgres user:
runas /user:postgres cmd.exe
7.) Run the install file from within the command window.
->his should run the installation successfully.
8.)Remove the postgres user from the Administrators group.
net localgroup administrators postgres /delete