QuickBooks Error 15240 is frequently brought on by improper system date and time settings, a lack of administration privileges, or interference from firewalls or antivirus software. It typically arises during payroll or software updates. Start by launching QuickBooks as an administrator and making sure the date and time on your machine are correct in order to resolve this issue. Make sure your payroll subscription is active and check your Internet Explorer settings, as QuickBooks depends on these for connectivity. Disable any security software that might be preventing the update process for the time being. Use the QuickBooks Tool Hub to run diagnostic tools or think about doing a clean QuickBooks installation if the problem continues.