Mods not properly loading

[Frad826]

I am having a problem with a modpack im using, it wasn't updated for a bit (25 days). As I launch the pack, everything is fine, it launches fine. Although the problem is when i join the game, the mods Mekanism and Fluid Mechanics are not in the game. When I look at the error log (lets name it error log 1), it states that the .jar files of these following mods are "non-mod file".

I then tried to take out the files because i thought they were outdated, so i take them out and put the brand new stable update for 1.5.1 (Mekanism-v.5.5.5.48) (since the modpack is in 1.5.1). But after doing that, the launcher crashes and send error log 2, which says fatal error and bla bla...

I am probably doing something wrong so I'm asking the pros out there, have any idea how to fix my problem? You can ask for any logs I link them, just don't want to put too much text in the main post!

Please help, this modpack seems really fun, me and my friends are counting on it! (PS: I will try to host a server, but the server has the same problem, no mekanism when i join)