Hey there, I just wanted to fill you in how I got around this error.
You need to add a launch command to the level editor in Steam, you should
not need to add the command to the actual game as well.
Right click on the
Super Meat Boy Level Editor and select
Properties. Then click
Set Launch Options and add the command,
-1024x768 and push okay. No quotes, just write it as shown.
Me thinks Team Meat should straighten this out, as I can imagine people punching their monitors in half just trying to get the silly thing to turn on. Just so you all know, my default resolution is 1280x1024. Not only is the game hard; turning the level editor on is even harder!
Edit: There seems to be a side affect of running the game in a lower resolution; notably that your mouse clicks aren't entirely accurate. You'll notice that your currently select tile will drift away from the cursor the farther away the mouse is from the center of screen. Selecting the buttons at the top of the screen also appears to be a bit tricky, though certainly doable.