1 duplicate symbol for architecture i386

Look at both the files for ClassX and ClassY - What targets are they included in? Basically the _selected method is duplicated in both of them. I am going to guess this is a plain C method that happens to be named the same in both files. Try renaming _selected in one of the files.

In my case, I was declaring a const in a header file, which worked fine when building and running on the device (iPhone 5), however when attempting to simulate a 4S, all of a sudden I had some 300 "duplicate symbols".

It turns out I needed to also mark the const as static and the issue went away. Presumably it was trying to redefine the constant every time the header was referenced. The compiler isn't smart enough to just make constants static? Didn't think that would be necessary, but I guess it is.

const CGFloat kTitleAnimateDistance = 50.f;

Needed to be:

const static CGFloat kTitleAnimateDistance = 50.f;