I think I figured out what was going on. When I replaced the config files I didn't delete them myself, I dragged them over and it asked me if I wanted to replace or something (I didn't really read it). I went in again and deleted the config files from every client and the server except for one and then copied the remaining files into all the ones that I deleted the files from. After running the server, to my satisfaction, I found this worked and now everyone can connect.
ID 31997 is mismatched between world and game ID 31996 is mismatched between world and game ID 31999 is mismatched between world and game ID 31998 is mismatched between world and game You cannot connect to this server. This is a lan server with the following mods installed on both cliants: SG Craft0.7.3 Grimoire of Gaia2 Atum1.6.4-0.5.9b Slenderman_V5 TheYouWillDieMod V0.0.3d I did a little research on this and many people said that it has something to do with the config files and I should copy one from one to the other. I already did this so please don't sugguest it. I also know that both clients have exactly the same mods, mod versions, and forge version. Any help is greatly appreciated and I will love the person for ever and ever that can help me solve this problem Thank you!