The title is pretty self-explanatory, I'll just drop the crash log and leave the rest to you.
Crash report

Update reborn core

Then you need to provide a minimal required version of reborncore in your mod.

This kind of issue is normally resolved by telling Forge (through mcmod.info I think) that you require version X of mod Y or higher, in which case it will be prompted explicitly to the user and not through a crash.