Minecraft 1.12
Forge 2389
Biomes oPlenty 2288

The game crashed whilst there was a severe problem during mod loading that has caused the game to fail
Error: net.minecraftforge.fml.common.LoaderExceptionModCrash: Caught exception from Biomes O' Plenty (biomesoplenty)

2017-07-03-7.log.gz
crash-2017-07-03_19.10.15-client.txt

Edit: Updated to 2288 and it works fine, no crash for me.

Same here on Forge 2389, MC 1.12, BOP 2274.
crash-2017-07-03_23.17.43-client.txt

using several versions of forge and biomes o plenty i've been having the exact same issue. please help?

oh! i did some more research and found out that the latest version of optifine hasn't yet been optimized for the latest version of forge. feel a bit silly as that seemed obvious, hope this helps!

Yeah, we don't support Optifine for this reason. It's explained in the issue template as well...

i get error forge + biomes o plenty, no other mods loaded nor resources etc ..biomes o plenty worked fine on MC 1.11 or 1.10 but not on 1.12, doesn't matter what version of forge or bop i try :(

In your case you're using an outdated version of the mod, you should be using 2288, not 2258 (as per your crash log)

In your original issue you noted that it's 2288, but that's definitely not the version that the game is loading. You might need to check your installation.