I just installed UltraEdit version 18.20.0.1028 on a fresh install of Windows 8 64-bit. I noticed the UltraEdit context menu in File Explorer was missing. I haven't solved it yet, but I've noticed if I turn UAC on the context menu returns and seems to function fine. With UAC on the 'Integrate with Explorer as:' inside Advanced / Configuration / File Associations works as expected and lets you toggle the context menu on and off. With UAC off that doesn't function and I can't seem to get it to show up. So I thought I would go back to my trusty reg file that I had used with previous versions of UltraEdit and other applications with similar issues.
However with UAC off and my asterisk class registry entry imported there are still problems. For instance if I right click a file that is already registered to AutoIt and select the UltraEdit context menu created from my registry entry, it prompts each time for a program to open the file with. So far, UltraEdit seems to be the only application I'm experiencing this type of issue with. Windows 8 has made some changes with file associations, so I'm guessing it has something to do with this.

By the way I'm disabling Windows 8 UAC with this registry key (0 is off and 1 is on):
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
EnableLUA=0

Moving the slider bar down in User Account Control settings doesn't disable UAC in Windows 8, it only hides the prompts which seems to be a horrible setting. In addition, disabling UAC with the registry entry I provided prevents any Metro applications from running.

Any ideas how I can leave UAC off and still have a functioning UltraEdit context menu?

I don't have access to any Windows 8 computer, so I can only post what must be done to use the 32 and the 64 bit shell extension of UltraEdit on Windows 7 x64.

UltraEdit v18.20.0.1028 registers the shell extension on Windows 7 x64 as you can do with copying following into an ASCII file, saving the file for example as Add_UE_ShellExt_x64_x86.reg and double clicking on the file to import the data to registry.
Attention: The paths to both DLLs must match with real location on your computer. Verify the existence of the DLLs.

To do the opposite and unregister the 32 bit and the 64 bit shell extension DLLs following registry snippet is needed:
The two DLLs are registered for the current user account only, not for all user accounts, to avoid problems because of missing write permissions for local machine branch and for multi-user environments where each user should be able to register the shell extension with a user specified menu item name.

As you usually work with UAC disabled, you use most likely an account with administrator privileges and therefore you have also write permission for HKEY_LOCAL_MACHINE. So if you want the shell extensions registered for all user accounts, replace HKEY_CURRENT_USER by HKEY_LOCAL_MACHINE before saving the file as REG file and importing the data.

The shell extensions do not contain the necessary data and functions to register itself which is the reason for the error message of RegSvr32.exe. The data to register both DLLs is inside uedit32.exe and not inside the 2 DLLs. Therefore RegSvr32.exe cannot be used to register the DLLs.

The HKEY_LOCAL_MACHINE version of the registry settings corrected the issue. Thanks! Don't know what they pay you, but it isn't enough.

Windows 8.1 x64 UAC disabled.
Can't register shell extension:
I've tried to do it using UEdit configuration - no luck.
I've tried using regsvr32 from elevated command prompt and I guess I've found what was the problem:

C:\Program Files (x86)\IDM Computer Solutions\UltraEdit>C:\Windows\System32\regsvr32.exe /i ue64ctmn.dll

But it displays error:
The module ue64ctmn.dll was loaded but the entry-point DllRegisterServer was not found.

Only above mentioned registry hack with HKLM works. I guess it should be fixed by IDM already!