Installed Open Blocks along with OpenModsLib on top of a lightly modded Vanilla Forge, and the client crashed while loading. I then tried again with ONLY Open Blocks and OpenModsLib on top of Vanilla Forge (version 1.2.1, forge version 14.23.0.24.86) and got the same crash. My crash log is attached.
crash-2017-12-17_13.54.35-client.txt

It requires recent-ish Forge (latest recommended should be fine). Is there any particular reason you are using 2486?

That's just what the Vanilla Forge modpack is using. I could try updating and see what happens, but I haven't done so yet because I figured there was a reason the modpack hadn't updated yet?

Ok. Anyway, latest update depends on few features, so can't fix that on my side.