Thread moved. ^^

The message you got is from an absence of a program called "Microsoft .NET Framework 4.5" It is a free plug-in from Windows. It was supposed to be put in Windows 7 but was removed because it was not completed. Now that is completed it is available to download here:
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Download it and install it, it should take 8-10 minutes, and retry it.

If all that doesn't work try these options:

-Re-downloading the software from its original forum under "How to Use" :
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-Write a comment on explaining the error and the picture you have to "Red-EyeX32" and see if he responds. Here is his account:
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Best of Luck! If all these don't work try a different application. Just look up "MW3 Multiplayer split-screen editor (Place Your Gaming Platform here)"

-David

(P.S. If it works and you choose specialist kill streak there is a perk known as "Marathon" DO NOT PUT THIS IN THE STREAK! You will get this error and you will have to reset the whole program: "Error: Cannot access a closed file." Keep this in mind when you edit your Multiplayer games!)