Do you have the link to the beta XCTU app you installed? I'm running released version 126.96.36.199 on two different Windows 7 machines, one 32-bit, one 64-bit, without error.
I do seem to remember one tricky thing about the install though, in that the XCTU install seemed to "stall" on me. It was at that time that I discovered a popup behind my XCTU install window (which didn't even show up on the Task Bar mind you), which was prompting me on whether or not I wanted to download the firmwares from the Website (if I remember right). Once I clicked the box and it went away, the install continued without a hitch.
Is it possible this is what you are running into as well?