I haven't been in Schutzhund very long and am only training my first dog for it, but I think your situation could happen to anyone training for anything so I'll give my opinion.........which is mostly to second what other people have said.
I know that it would probably be really frustrating, but if it were me, I would take a few sessions to just go out and play and bond and have fun and act silly together and not do anything else at all. If you live close to the training field and have time you could do it several times a week and probably get him over it sooner than if you just waited for the normal club training day each time.
Have you seen any of the Michael Ellis training videos? I love, love, love him and his methods. "The power of training dogs with food" is GREAT and it really helped me get my dog extremely focused and engaged on me, and I think this is partly at least because I make it fun and less like boring work. I actually sent an OB training video to my dog's breeder for her to evaluate and see our progress and she commented on how focused my pup was (and I've only had her like 2 months maybe now? she's almost 9 mths old), and this session was outside in our yard with numerous distractions.
When I first started working with my pup, I actually spent a few of the first training sessions just working on engagement, focus, and luring and even in subsequent sessions until just recently, I would start them with the engagement/luring/focus work for the first 1/2. I kept each session short, maybe 2-3 min to start and worked up to about 5-6 min now.
Positions, behaviors, tricks, etc. are relatively easy to teach really.......getting your dog engaged and focused on you is the hard part so I think it's worth it to spend time working on only that. My video is on youtube if you'd like to see it to get an idea of the way Michael Ellis teaches obedience.
I also know that when I start getting frustrated with my pup, she KNOWS and will act accordingly (which is not in a good way!). So if I ever feel that feeling coming on, I just start praising my pup even more, encouraging her to jump up on me (she really likes this
), and petting her and keep moving forward.