You could try clearing cache and data from app to see if that helps.

Settings > More > Application Manager > flip screen to 'All'
In there you'll find two 'Samsung WatchON' apps, for both select them then 'Clear Cache' and 'Clear Data'.

Note that if you've set up any rooms that this will wipe them out, but since you can't get in to the app at all right now that probably doesn't make a difference.

If your phone is rooted, you could also try a 'Fix Permissions'.