Windows 8.1 is no longer a "beta" release.  It is now a full upgrade and new PC's come with Windows 8.1 installed.  If you buy a new copy of Windows 8, it will be Windows 8.1.   
 
My "production" system is X3 on Windows 7 64 bit.  I originally installed X3 on Windows 8 to see how it would run (it worked OK), on my dual boot (separate drives) Win 7/Win 8.  The Windows 8.1 upgrade caused the problem, for some, not all. 
 
I also needed it to work as my backup PC is Windows 8.1 and Sonar X2 (c or d I don't remember - whatever the last update was).  It had the exact same problem and the exact same fix.

DeeringAmps
Why is anyone running win 8.x anyway???
8.1 is a "new" release, right?
You're having problems; really?
duh
Don't take it personal, but in my world the DAW is not the place for the latest
beta release...
 
T
 

 
For me - - - Some older legacy music software works better on 8.1 than 8.0. I learned this while trying out the 8.1 preview release. So a no-brainer decision here to get on the most stable and updated version of Win 8 which is now 8.1.

"My "production" system is X3 on Windows 7 64 bit."So is mine.
Musicroom, I'm glad 8.1 is working for you;
I'm gonna wait till the bugs are worked out...
 
T

I'm really liking the Win8.1 experience. Matched with Sonar X3c it's the best thing since sliced bread.

Since I got X3c 64 bit working on Win 8.1, I've done some recording, adding VST's and it all works, for me, exactly like X3c/Windows 7 64 bit.
All my hardware works with 8.1, including my old trusty Frontier Tranzport unit, that i had to install (in Windows 8) in a Vista compatibility mode, The Behringer BCF2000 is plug and play in Windows 8/8.1.  The MAudio Fastrack Ultra 8R did not require a new driver.  The only driver update I had to do was for the Roland Octa-Capture, with the new 1.52 driver that was issued for Windows 8.1. 
 
There is a discussion on the Windows 8 forum about PC hardware support in 8.1.  It looks like some older hardware that was Windows 8 compatible is no longer 8.1 compatible.  But these are older motherboards or PC's that were developed in the XP or early Vista era. 
 
 
 
 

I had the same error installing X3x64 on my StudioCat today (see below)

Windows tried to force a re-start, which I cancelled, then selected "Retry" and the install completed.
This is under Win 7x64.
Everything seemed to work OK after the install.
WTF?
 
Tom

I had the exact same error.
You need the VB update as previously noted.  That fixed mine, and others with that problem.

Thanks for that Fireberd.
If I have any issues installing X3c I'll run that down.
 
T

This is the update that's needed.
 
http://www.microsoft.com/en-us/download/details.aspx?id=30679

Thanks