Hello and yes we again resolved an issue for you, I have come to know that after installing Windows 8.1 Preview, it gives compatibility issue with SDK 8.0,  in result Windows Phone 8 Emulators does not run and give pointer error , basically that is due to the very problem of compatibility.

How can we resolve it?
How can one run Windows Phone 8 Emulators on  Windows 8.1 Preview?

Here is a nice tutorial,

When you install SDK 8.0 it will give you following message,

If you run it after ignoring it, you will find that Windows Phone 8 Emulator does not works,

You can resolve it by installing Update 3 of Visual Studio,

Here you go,

The story does not end here. Even after installing VS Update 3 you may get this error

HRESULT: 0x89721800 

Well if this occurs you would not be able to run any emulator and at device selection 
START will be displayed only,

There are two solutions for resolving it.

The only hint I found is the following:

If you get error code 0×89721800 when attempting to deploy to your phone device, this typically indicates that the Visual Studio datastore is corrupt. Here are a couple of workarounds:

Workaround #1
1. Close all Visual Studio instances that may be currently running.
2. Delete the folder “%LOCALAPPDATA%\Microsoft\Phone Tools\CoreCon\10.0”
3. Launch a new instance of Visual Studio

Workaround #2

The above error code has also been reported when Windows Mobile 5x or 6x emulators are installed in the system. Try uninstalling them both.

So I would give this a try, clean out all the folders under

LOCALAPPDATA%\Microsoft\Phone Tools\CoreCon 

and in case this would not help, then uninstall the SDKs and re-install the latest one for WP 8!

Further the following link points to other (WP8) Emulator (XDE) Troubleshooting Tips

Alternative Workaround:
Open File Explorer:
Open this path:

%LOCALAPPDATA%\Microsoft\Phone Tools\CoreCon\

Now delete 10.0 and 11 named folders and others from this path.

Note: Before doing all the procedure close all instances of Visual Studio

Let us know if that helps you to get the 7.x / 8.0 emulator working on your dev PC.

See Also

Another important place to find a huge amount of Windows Phone related articles is the TechNet Wiki itself. The best entry point is Windows Phone Resources on the TechNet Wiki.