I don't see anything significantly different from your code and Summerfield's, except for your failures to check if the QLineEdit pointer returned from qobject_cast is non-null. Sure, it *shouldn't* ever be null but what happens if it is?

My guess is that something in the code that you haven't posted is causing some stack corruption, and the error just happens to manifest itself when you get to that part of the code.

Please use CODE tags when posting source code - see my signature block for how to do that.