If you know the Mac OS application which can work as QBB file opener you can choose the 'Choose Application.' option in the error box to associate the file extension and open QBB file in it.If a QBB file is not opened in a Mac OS application and you instead get a 'There is no application set to open the file' error message you can click on 'Search App Store' in the error dialog and Mac OS will show you applications compatible with QBB file.Find a QBB file in question in Mac OS Finder and double click on it to launch the corresponding application.