When installing QuickBooks Desktop (or updates for QuickBooks Desktop), the following error message is displayed:
QuickBooks is currently in use: The Installation Wizard has detected that QuickBooks is in use in another user session. Please close QuickBooks and try again or cancel to exit.
Quickbooks Desktop is still running in the background or the Fast User Switching is enabled.
Either reboot the computer, stop QuickBooks Desktop from running in the background using the Windows Task Manager, or log in as the user with Fast User Switching and close QuickBooks Desktop.