I was replacing the Barrel adjuster on my gears, and the gear cable while I was at it. That went ok. Then I did a full check of the brakes while I was at it, to find that the back brake cable wasn't tight enough. Attempting to tighten it just sent the bolt spinning around.
Balls. No rear brake.
So, a trip to the LBS to get some new brakes. I changed the front one as well, as it was the same age (over 10 years old) as the rear, and I'm doing a hilly ride next weekend.
Still, it cut into my riding time, which I was a bit grumpy about.