If you get an error message when loading the XML, that means it could not be loaded, and you should get a screenshot of the error, and get it to me asap. If you let it overwrite your XML file, and you didn't have a backup, it's gone. I don't imagine you got any info on the error so there's nothing for me to go on to fix whatever it was

To back it up, for future reference, just use the Save As option from the File menu. This changes ISBoxer to use that file for autosaving, so you might want to switch back to ISBoxerToolkitProfile.XML afterward (by either using Open, or Save As). The file being edited is shown in the title bar (and on the "ISBoxer" config panel)

You could have continued using your lost config indefinitely -- until you Export again.