Just figured it out...
Update the modpack's lwgjl files and it'll work
P.S. Let more people know about this please, cause there are heaps of threads about this...
I have the same problem, but voltz is fine (which I played previously before this issue came about)...
Any other pack which I have recently downloaded just doesn't work...
EDIT:I just updated voltz and it doesn't work anymore (nooo...)