(Decided to take this out of comments and put it as an answer, since I think it’s a darned good answer 🙂
Ha! I had an NaN calculation (div0), too. Key debugging aid: the message in question is output by NSLog(), so set a breakpoint on NSLog() and watch what the OS is doing at that time. For me, it was myUISlider.value = NaN.
To set breakpoint:
XCode 3.x
- CMD-SHIFT-Y (debug window.)
- Breakpoints button.
- “Double-click for symbol”
- Type in “NSLog” (no quotes.)
XCode 4.x
- CMD-6 (breakpoints navigator.)
- “+” to add breakpoint (lower left.)
- Select ADD SYMBOLIC BREAKPOINT.
- Symbol: NSLog
- Confirm: Done.
XCode 5.x – 7.1 (at least)
(Same as 4.x, except breakpoints navigator is CMD-7, now.)
Run app, watch it break on NSLog, check the stack traces.