Troubleshooting MQL5 SocketConnect Error 4014 When Connecting to Local TCP Server

Use this when MQL5 SocketConnect returns error 4014 while targeting a local TCP service.

Quick Read

Symptom: Use this when MQL5 SocketConnect returns error 4014 while targeting a local TCP service.
Check first: Capture the affected source, destination, protocol, port, DNS name, VLAN or subnet, and exact error before changing policy.
Risk: Changes system state

Symptoms

MQL5 SocketConnect fails with error 4014 when attempting to connect to a local TCP server.

Environment

MetaTrader 5 (MT5) trading platform with MQL5 programming environment, local TCP server setup.

Most Likely Causes

Error 4014 indicates a failure in establishing a connection to the specified TCP server, often due to incorrect server address, port configuration, or firewall settings.

What to Check First

Capture the affected source, destination, protocol, port, DNS name, VLAN or subnet, and exact error before changing policy.
Verify path, name resolution, authentication, and firewall policy separately so one symptom does not hide multiple failures.
Check whether the issue is isolated to one client, one subnet, one VPN profile, or every path.

Fix Steps

Verify TCP Server Status
Ensure that the local TCP server is running and listening on the expected port.
Example pattern only. Adjust for your environment before running.
```
netstat -an | findstr LISTENING
```
Check Server Address and Port
Confirm that the IP address and port number used in the SocketConnect function are correct.
Example pattern only. Adjust for your environment before running.
```
Print('Connecting to: ', serverAddress, ':', serverPort);
```
Test Connection with Telnet
Use Telnet to test the connection to the TCP server from the machine running MT5.
Example pattern only. Adjust for your environment before running.
```
telnet <serverAddress> <serverPort>
```
Review Firewall Settings
Check the firewall settings on the local machine to ensure that the port used by the TCP server is not blocked.
Example pattern only. Adjust for your environment before running.
```
Windows Firewall: 'Control Panel' > 'System and Security' > 'Windows Defender Firewall' > 'Advanced settings'
Add inbound rule for TCP port <serverPort>
```
Inspect MQL5 Code for Errors
Review the MQL5 code to ensure that the SocketConnect function is being called correctly.
Example pattern only. Adjust for your environment before running.
```
Socket = SocketConnect(serverAddress, serverPort);
if(Socket == INVALID_HANDLE) { Print('SocketConnect failed with error: ', GetLastError()); }
```
Check for Multiple Instances
Ensure that there are no other instances of the application trying to connect to the same TCP server, which could cause conflicts.
Example pattern only. Adjust for your environment before running.
```
tasklist | findstr <applicationName>
```

Reference Command or Script

Example pattern only. Adjust for your environment before running.

void OnStart() {
    int socket = SocketConnect('127.0.0.1', 8080);
    if(socket == INVALID_HANDLE) {
        Print('SocketConnect failed with error: ', GetLastError());
    }
}

Validation

The same client and network path can reach the target after the change.
Firewall, VPN, DHCP, DNS, or switch logs show allowed traffic or successful negotiation instead of the prior failure.
A second path check confirms that the fix did not open unintended access or break another subnet.

Logs to Check

Firewall, VPN, DNS, DHCP, or switch logs for the failing timestamp.
Client resolver, route table, VPN client, or browser/network diagnostics.
Packet capture or flow logs when policy and routing disagree.

Rollback and Escalation

Export or screenshot the original policy, route, resolver, or interface configuration before changing it.
Remove temporary allow rules, test DNS records, or route changes after validation.
Restore the previous VPN profile, firewall rule, or switch configuration if reachability worsens.

Escalate When

Escalate if the same error persists after rollback and a clean retry from the original failing path.
Escalate if logs show authorization, data loss, certificate, replication, or production availability risk outside the local service owner scope.

Edge Cases

Server not configured to accept connections from localhost.
Incorrect protocol (TCP vs UDP) being used in the connection attempt.
Antivirus software interfering with the connection.

Notes from the Field

Most network incidents need source and destination evidence. A successful test from an admin laptop does not prove the affected client path is fixed.
For VPN and firewall changes, keep the blast radius narrow and time-box any temporary allow rule.