Catrin, this may sound like a kooky question but are you turning your handle bars enough to get through a switchback? This question comes from my own personal experience. I was initially trying to get through tight turns on my mountain bike by leaning as much I do on my road bike. My handle bars were usually pointed almost straight ahead regardless of how tight the curve was. I started negotiating switchbacks better once I started turning my handle bars more.

Speaking of switchbacks, I had forgotten about focusing on where I wanted to end up rather than looking just ahead of my front wheel on switchbacks. Today I focused on the exit of a couple of tricky switchbacks and rode them faster and much more smoothly than I've ever been able to do in the past.

I'm anxious to use this focus trick on a switchback that stumped me on my last ride. I tried that switchback three times and kept stopping at the same spot. Now I know that I was looking at the apex of the curve where I was mostly likely to ride off the trail. Sure enough, my bike started heading off the trail every time I approached that spot. I'm pretty sure that I can ace that switchback next time by focusing on the exit of the curve rather than the apex.