Hello

When launching the animation of the tennis ball in the first part of this chapter, trying to move the slider causes the app to crash. The file downloaded from WROX seems to have the same issue.

Any thoughts?

Did you ever resolve the crashing problem? It is working fine for me, as is the downloaded code.
Originally, I did have a crash, but that was caused by a typo on my part in the IBAction method. Maybe something similar occurred in your project. What messages are you getting in the console?