Lua: Loading a Lua script through a wad

So basically, In a wad file I have a Lua script under the filename of LUA_BSLM.
It loads a thinker for my custom blue slime object, but whenever I load the wad into the game I am always getting this error:
WARNING: SlimeTesting.wad|LUA_BLSM:7: mobjtype 'MT_BLUESLIME' does not exist.

What does this mean? I have my object as MT_BLUESLIME in my MAINCFG inside the wad, but for some reason, it cant detect it or something.

I am also having the same problem with my LUA_RSLM (Same as LUA_BSLM, but for my red slime object MT_REDSLIME) I get the same error, but instead of MT_BLUESLIME it says MT_REDSLIME.

Here is the wad if anyone could care to take a look at it:
https://www.dropbox.com/s/6ph4h2f6to8tl6g/SlimeTesting.wad

Thanks in advance for any help provided.

EDIT: People on the IRC helped me fix this recently, please lock this.