UPDATE: I installed a fresh copy of Blockland, because all of the stock Add-Ons work. I then tried to add Add-Ons one by one and when I added one vehicle, it got rid of all the other vehicles. I also added IGSO and FFC and they didn't work.
It is also is interesting to note that all things dealing with files are case sensitive, as in, the folder is called "Add-Ons" and someone packaged a mod and named it "Add-ons", well, it makes another folder beside Add-Ons called Add-ons. I tried changing the case of all the folders and the main one, and it still didn't work.
Halp.