Can't connect to my Aternos fossils and archaeology server.

Hi all. I recently noticed Aternos FINALLY added FnARev, and it being my favorite mod I installed it, and got the mod for the server. I've tried quite a few times but for whatever reason I keep getting the same error message over and over (error message screenshot in attachments) I downloaded an FnA installer and it launches fine, works in singleplayer, etc, but won't connect to my server. I tried going through Aternos and downloading the mod(s)[FnA, and LLibrary) getting forge, etc, but crashed on launch. I also saw in the server list that there's a check mark next to the aternos server saying 'mods compatible' but once it launches, it became a red X and says 'mods not compatible, 5 mods active' or something along those lines. I was very confused and because FnA is a 1.7.10 mod, I decided to try and connect on plain old vanilla 1.7.10 and it actually (sort of) worked. I am able to ""connect"" to the server, but it never actually joins, just sits on the 'logging in' screen and makes pretty much no progress. Is there something I'm doing wrong???? Something I'm missing?