So First time when I downloaded the file, it worked perfectly. No error message, No crashes, and No corrupts. Until when I added one 3 mods in, the file got corrupt and stopped working with an error message saying that the file is either corrupt or invalid. Now everytime i download it, the same error pops up everytime i run the jar file for me to check if it works. if you have a solution to this problem, I would appreciate it. Also Jarfix didn't fix it at all so you know.

Don't know what to tell you. The jar is not corrupted, that much is certain. So it's an issue between you and Curse. You'll have to get with them.