x40 on what these guys said

That's a 1 ounce lure your tossing around with 12# fluoro.. I'd bet its a shock related breakage esp if you have a snappy cast to try to get that lure out there for a longer cast.

Else like others said, check all the guides. 

If you like Fluoro I'd go with Seaguar Tatsu .. its been very durable for me..

Check the guides as others have said and don forget the line guide on your reel too! That's where mine was and I couldn't figure it out why it was fraying my line for the life of me haha. Also try changing your knot, that may be the problem also.