I'm not particularly experienced with modding and the constant version updates and everything have my head swimming when it comes to trying to mod anything with this game and it usually involves hours or days of headaches trying to figure out what's wrong. 

 

Anyways, I'm trying to start up a 1.7.10 world with Sonic Ether's Shader Mod.  That's the end goal.  I downloaded 1.7.10.  I downloaded Optifine for 1.7.10.  I downloaded Forge for 1.7.10.  Said it installed fine, but when I hit play, I get a java.lang.AbstractMethodError or something.  Don't know what on earth this means or what to do to fix it.  Not sure how I attach documents to this, but here is a picture of the error screen:

 

 

Any help would be appreciated.  Might not be able to respond back immediately cuz I wasn't thinking this would take hours and I'll have to be away for a bit.

 

 

 

You have a coremod installed that is not for your version of minecraft you will need to look at your mods folder and find out what.

Yup, thanks!   

 

So how do I hold onto mods for old versions?  Do I just have to swap in the mod files/folders everytime I want to play on an older game?

/mods/1.6.4 , /mods/1.7.10 , etc

 

Or just use the Game Directory option in the launcher.