QuickBooks Error 15106 is related to problems with updating QuickBooks. To resolve it, first, make sure you're logged in as an administrator. Disable User Account Control (UAC), or run QuickBooks as an administrator. You may also need to perform a clean installation of QuickBooks. This involves uninstalling and then reinstalling the software, ensuring that you've turned off any security software that might be blocking the update. If the error persists, reach out to QuickBooks support for further guidance.