How to fix Error 1220 on Windows 11

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Troubleshooting Guide: Error 1220 – “Too Many Sessions Established to Server”

Why This Error Happens

Error 1220 occurs when a client attempts to establish an SMB (Server Message Block) connection to a network server, but the server has reached its maximum limit of concurrent sessions or connections from that specific client. This is typically caused by orphaned or “stale” SMB sessions that weren’t properly closed after previous connections (due to abrupt disconnects, crashed applications, or network interruptions), which continue to consume session slots on the target server. It can also occur when a server’s MaxMpxCt or session limit configuration is set too low for the number of concurrent connections being requested by client machines.

Step-by-Step Resolution Guide

  1. Clear existing SMB sessions on the client machine
    Open Command Prompt as Administrator and run:
   net use * /delete /y

This forcibly disconnects all mapped drives and active sessions to network servers, clearing stale connections.

  1. Check and terminate lingering sessions using PowerShell
    Run PowerShell as Administrator to view and remove specific SMB connections:
   Get-SmbConnection
   Remove-SmbMapping -Force

Identify the problematic server and remove any duplicate or orphaned mappings.

  1. Increase session limits on the target server (if you manage it)
    On the server (Windows Server or a Windows 11 machine sharing files), open the Registry Editor (regedit) and navigate to:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters

Add or modify the DWORD value MaxWorkItems and MaxMpxCt (increase to 2000 and 800 respectively, if not present) to raise the session/connection threshold. Restart the Server service afterward:

   net stop server
   net start server
  1. Restart the Workstation and Server services on the client
    This clears the client-side session cache without requiring a full reboot:
   net stop workstation
   net start workstation
  1. Update SMB-related network drivers and Windows
    Ensure the network adapter driver is current via Settings > Windows Update > Advanced Options > Optional Updates, as outdated NIC drivers can cause improper session teardown.

Alternative or Verification Steps

  • Verify the fix: Reconnect to the network share (net use \\servername\share) and confirm the connection succeeds without triggering Event ID 1220 in Event Viewer > Windows Logs > System.
  • Alternative: If the error persists across multiple clients, check the server’s Srv.sys event logs for MaxMpxCt warnings, and consider load-balancing connections across multiple server endpoints or increasing hardware resources if session limits are consistently maxed out due to legitimate high demand.