I’m sorry, I don’t understand what you’re trying to achieve. What’s a GtkFileSelectorDialog, and what does it have to do with a combo cell renderer?
You’re trying to set a property on an object that does not have it; you’re probably misusing the cell renderer API, or you’re trying to force a state that does not exist. Since you’re not pasting your code there’s not much that can be done.
You can try using GDB and export G_DEBUG=fatal-criticals in your environment, in order to get a backtrace.
I assume the double $filesel->run is a copy-paste issue, but in general this is a terrible idea to begin with. You’re creating a modal, blocking dialog on top of a combo box menu, which is modal on its own, and has its own share of grabs and side effects. You’re also doing so in the middle of the changed signal handler, preventing it from completing. Once you close the file selection dialog (which you should do regardless of the response id, otherwise it’ll never go away) the combo box menu may have gone away.
I suggest you move the creation of the file selection dialog into an idle function, to let the rest of the UI behave like it should. If I use this: