I am having this exact same issue. Hopefully I can expand on the issue some more.. The OP is slightly vague. Also, after typing all this up, I found a solution. 
So hopefully this will help everyone else down the road.
The highlights:
* I have TUC on Origin.
* I have the fixed custom launchers. (what a godsend, btw)
* I can launch the custom launcher WITHOUT C&C Online no issue (no hooking) and am able to select the mod (Upheavel in this case) and it loads just fine. This is accomplished using a shortcut to the RA3.exe file and appending the " - ui" to the end of the Target.
* I can launch the standard launcher WITH C&C Online (with hooking) with no issue and can play online just fine. This is running the RA3.exe directly. No shortcut, no " -ui" appended or anything. Plain jane vanilla RA3.
The issue is that I can't use the custom launcher with C&C Online (with hooking) to play the mod online. I just get the same error message above "Unable to launch Red Alert 3". So I can play online as vanilla, or I can play offline with the mod, but not online with the mod.
After checking the error log as described in the sticky mentioned above by ToxicShock, it had the following in it:
----- C&C:Online Launcher Start -----
Game: Red Alert 3
Red Alert 3 Install Path: E:\Origin Games\Command and Conquer Red Alert 3\Red Alert 3\
ERROR: CreateProcess() failed to start E:\Origin Games\Command and Conquer Red Alert 3\Red Alert 3\RA3.exe. Error: The requested operation requires elevation.
ERROR: Unable to launch Red Alert 3
Well it says "The requested operation requires elevation." SO! What I did was I ran the SHORTCUT with the " -ui" appended as administrator WITH HOOKING ENABLED in the C&C Online launcher. Sure enough, once I do that, the C&C Online launcher pops up, I click Red Alert 3 and it loads the customer launcher version for me where I select the mod, as if I was running the shortcut without hooking and not as administrator. I am then able to log in to the "GameSpy" servers as if I was running vanilla RA3.
Hope this helps everyone else.
EDIT:
To avoid having to right click and "run as administrator" every time you want to use your shortcut for this, you can go to the Properties of the shortcut (Right Click -> Properties) then clicked "Advanced..." from the Shortcut tab (should be loaded by default) then just check the "Run as administrator" box. Then apply and hit ok and voila.
Edited by Cooper_Atlas, 26 March 2015 - 03:48 PM.
