To resolve QuickBooks Error 15240, begin by updating QuickBooks to the latest version. Confirm accurate system date and time settings, ensure a stable internet connection, and adjust firewall settings to permit QuickBooks access. Temporarily disable User Account Control (UAC) and validate an active payroll subscription. If the error persists, consult QuickBooks support or the official community for detailed troubleshooting steps. Follow these guidelines to efficiently fix QuickBooks Error 15240 and ensure seamless software functionality.