My guess is that your program has corrupted the stack or heap somehow, and that the error throws the execution into some random place in the executable, in this case the library that contains the QString code. It is undoubtedly a red herring, and the error that causes this is somewhere else *in your code*, not in QString.

As anda_skoa says, post something useful, like a stack trace (not an unreadable screenshot of a stack trace, the text itself). Better yet, examine the stack trace yourself to see where your code calls into the Qt library. The error is likely to be somewhere in that code. If it isn't obvious, run the debugger, set a breakpoint in your code shown in the stack trace, and examine all of the variables being used at that point (including "this" if you are in a class method) to see if they make sense.

Happy hunting.