This particular error occurs when I try to use "//set 'block'".
The only map that this occurs on is a map I created a year ago for a server. The other map I tried that I created a few weeks ago works perfectly fine with world edit. I have tried uninstalling and re-installing Minecraft, Minecraft Forge, and World Edit, but all have failed because the error occurs every time. I think the error is something to do with the specific older map that I used an older version of worldedit and MCEdit on.