It's the Microsoft .NET Runtime Execution Engine (ie makes a lot of modern applications work.)
Here is one place you can download it from, but there are many.
You will need to unzip it, put it in C:\Windows\System32 (that's a guess, but it doesn't really matter) and then do Start, Run:
RegSvr32 c:\windows\system32\mscoree.dll
after which you should get a message "MSCoreE.DLL successfully registered"
I don't have ME, nor would I allow it in the building, even if it wiped its feet, so I can't check the above, but it should be OK.
W