I’m running C7 7.0.3 / I am trying to install the latest update 7.0.4 but keep getting Error code 1603 / Fatal Error during installation ? Can anyone help with this ?
By the way I have W7 Pro, 64bit
I think this can happen if your current install has been corrupted.
You may be able to repair using the 7.03 installer but best option is probably to un-install and start from scratch installing the 7.02 complete installer and then the 7.04 update.
you can also choose the repair function on the 7.0.2 if you wish to repair 
I got this when i tried to install 7 updates after removing 6.5
I just rolled back but this is repeatable here, remove 6.5 after 7 is installed and 7 will fail to update to 7.04 with error code 1603 with the 64 bit version of cubase.
Hippo
This happened to me too. I don’t understand why it is always a Steinberg product that causes such problems.
Easiest way to solve the problem:
Rename the folder c:\Program Files\Steinberg\Cubase 7 (Cubase 7-xxxxxxx)
Install the Cubase_7_Core_Installer_win.exe (You find it on the download page)
Install Cubase_7.0.4_Update_win.exe
Copy the old plugins folder …\Cubase 7-xxxxxxx\VSTPlugins to the new Cubase 7 folder
Delete old Cubase 7-xxxxxxx folder
Nothing lost, and everything works…