Frustrated? Feeling like it will never happen? Just walk away, really, just get up and take a hike!
We're taught to hang in there, tough it out, and it will get better, and while I agree to a point , I firmly believe we all need separation from things that frustrate us. While I say walk away, within a few minutes you ought to walk back and give it another go, but definitely DO NOT simply pick up from where you were...find a new approach, something that's different from the way you were doing it (which wasn't working, remember?)
It can be as simple as drastically altering the tempo (slower OR faster) to gain a new perspective on the music, although you need to bring the tempo down again (Rule #1 - if you can't play it slow, you can't play it fast!). That momentary change can be enough to overcome the obstacle you ran into before you walked away. The trick is to find something that's different, and here, the best advice I can give you is: experiment. Don't be afraid to try something really goofy, it may just work!
If we get out of our heads and let our bodies do what they are truly capable of doing, usually we end up being successful, so...the next time you hit that wall, don't keep bashing your head against it, get creative, paint a picture on it, or in other words, find a way to do something different to take your mind off the problem. Good luck!