Hi Paulette--
You can use the window_class() function to check the type of window before calling window_destroy() on it, to prevent your code from completely closing the application, something like this:
...
if (window_class(win)!="edit") {
window_destroy(win);
}
...
When working with custom dialogs, be sure not to get the dialog window confused with the main editor window, and correspondingly, the XUI document for your custom dialog vs. the document currently open in the Editor window.
As for debugging, it can be helpful to insert response() function calls at key points in the function that is failing. That can tell you how far the code is getting before it fails.
--Clay
