When I upgrade to 1.6-43 from 1.6-42 I get this message when I try to load any save.

Errors in currently selected datapacks prevented world from loading. You can either try to load only with vanilla datapack ("safe mode") or go back to the title screen and fix it manually.

I removed all my datapacks and all my resource packs but that didn't work. The only way to play is revert back to 1.6-42 and older Quark. Yes, I have many other mods. Yes I have Optifine. I tried with forge 32.0.75, 32.0.77, 32.0,90 and 32.0.93

Can confirm this issue persists even if autoreglib and quark are the only installed mods.

I’m getting this problem too and I can’t play because of it

I’m getting this problem too and I can’t play because of it

you can downgrade to 1.6-42 assuming that you aren't running forge 32.0.90 or later

You can sort this by updating to the latest forge, no downgrading of versions required.