When users attempt to open QuickBooks in single-user mode when another person is using it, they may see the error 80040408. Seeing it can be annoying, particularly when there is a lot of work to be done. So let's investigate rational fixes to get rid of this issue and get a flawless QB experience. If you require quick help and guidance, don't hesitate to contact the QuickBooks Support Team directly at 1.855.738.2784.