The most probable reason is an invisible invalid character somewhere in your code, probably between nil
and cancelButtonTitle
.
Remove the two lines entirely and write them again.
The second possibility is doing something really bad with macros, e.g defining a macro
#define cancelButtonTitle @"Cancel"
There is a reason why all macros should be written in uppercase letters:
#define CANCEL_BUTTON_TITLE @"Cancel"
And it would be even better not using macros for string constants.