I looked around through this forum post as well as the ModDB comments and I've seen a couple people with similar issues but I didn't see any fixes for it (sorry if you've already replied to them, I just didn't see them)
I was running xSkills 0.8.7 and xLib 0.8.4 along with several other mods just fine as singleplayer, but when I opened to Lan to allow some friends to play they would immediately crash to desktop when trying to connect to my world, receiving an error message mentioning an issue with xLib. Unfortunately, my friends are just a tad computer illiterate so I haven't been able to get any more info out of them. Everything works fine without xLib and xSkills installed.
My current mod list, in case it would help. Keep in mind, it all works great for me in singleplayer, it just won't allow people to join in multi.