I really find it annoying when people act like asshats in the Help forum. It's the one place you really shouldn't be messing about. Go back to Off Topic you filthy vermin.
Anyway mr conrs, I'd suggest making sure that you extracted the M16 add-on correctly. You're meant to extract the .zip file to the C:\Program Files\Blockland folder, nowhere else. If you can't manage to do this for whatever reason, Just untick the M16 add-on in your list so you can play again. Its really not one of the best weapons on Blockland so I wouldn't keep trying to make it work.