Go into your Direwolf20 folder. Go to saves. Take everything out and put it somewhere easily accessible and somewhere temporary. Delete the entire Direwolf20 folder. Play the Direwolf20 mod pack from the launcher, and it'll download it again (an updated version will be downloaded -- there's no worry of having to manually update it). Go into your new Direwolf20 pack, go to saves, and dump the worlds from your last Direwolf20 pack in there. Close it all out, and launch the Direwolf20 pack.
If that doesn't work, then it's probably something affecting it (such as a mod you're using that may be incompatible, or some other kind of incompatibility).
Hope this helped.