Problem with Limit Break

I can't use my Limit Break in dungeons. I'm a Arc/Sum and since my first dungeon I have tried to use the limit break and have not been able to. The Party will have full Limit bar(s), and when I try to use it, it says "Cannot use yet" or "Cannot use while casting", however I'm not casting anything. I have tried multiple times to use the Limit Break and got nothing. I have had other people in the party ask me to use my limit break and I respond that I tried and nothing happens. Thanks