When you download the add-on, DON'T uncompress, unzip, take the files out or anything. Leave the file as it is downloaded and do not touch this. Simply drag it into the Add-Ons folder which is located here on steam:
C:\Program Files (x86)\Steam\steamapps\common\Blockland\Add-Ons
Located here on non-steam:
C:\Users\*UserName*\Documents\Blockland\Add-Ons
Just put the .zip file which should be named something like: 'Weapon_Gunname' Or 'Client_script'
