error 789

Error 789 is a common Windows VPN connection failure code, typically associated with L2TP/IPSec setups. On WindowsForum.com, users troubleshooting this error on Windows 11 have explored solutions such as adjusting the AssumeUDPEncapsulationContextOnSendRule registry key, enabling ProhibitIpSec, and verifying firewall ports 500, 1701, and 4500. Other steps include reinstalling network devices, enabling MS-CHAP v2, and checking LCP extensions. The error often appears in Event Viewer with the message 'the user system dialed a connection named VPN name which failed.' While some fixes work on one machine, the same configuration may fail on another, suggesting driver or system-specific issues. Reinstalling Windows or resetting network components are last-resort measures discussed in community threads.