EP installers not working

Hi! I'm sorry to be a bother but none of the installers seem to be working on any of the EP files I've downloaded. I've tried everything that I could find in the forums but nothing seems to be working. I keep getting the message in the image below and I'm not really sure what to do. I've tried opening the .exe file as well as stated in the installation guide.txt but it only shows me a certificate of some sort? Any help would be very much appreciated.

(Also apologies if this is already asked question. I couldn't find anything relating to it ><)

//EDIT

I forgot to mention that I've also tried the whole .dmg thing. Still nothing 

Hello TheAvatar,

I'd like to remind you one thing before answering your problem. Please use edit button whenever you want to update your current post. Thank you so much!

I have some questions for you to idetify your problem: Did you download the expansions from G4TW? Have you created a working .dmg files? Was your main game working before you attempted to install the expansion packs?