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Title
Connection error: "A network-related or instance-specific error occurred while establishing a connection to SQL Server." -
Description
Connecting Toad to a SQL Server instance gets error A) below. Connecting Server Management Studio (SSMS) also gets the same error; see error B) below:
A)
ERROR FROM 'ExceptionTrace.log' FILE:New exception: 12/17/2014 4:36:20 PMSystem.Data.SqlClient.SqlException: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)Stack trace:at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection)at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning()at System.Data.SqlClient.TdsParser.Connect(ServerInfo serverInfo, SqlInternalConnectionTds connHandler, Boolean ignoreSniOpenTimeout, Int64 timerExpire, Boolean encrypt, Boolean trustServerCert, Boolean integratedSecurity) .....B)ERROR FROM SQL Server Management Studio (SSMS):===================================Cannot connect to TRAINGEN.===================================A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server) (.Net SqlClient Data Provider)------------------------------For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft%20SQL%20Server&EvtSrc=MSSQLServer&EvtID=5&LinkId=20476------------------------------Error Number: 5Severity: 20State: 0------------------------------Program Location:at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection)at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning()at System.Data.SqlClient.TdsParser.Connect(ServerInfo serverInfo, SqlInternalConnectionTds connHandler, Boolean ignoreSniOpenTimeout, Int64 timerExpire, Boolean encrypt, Boolean trustServerCert, Boolean integratedSecurity)at System.Data.SqlClient.SqlInternalConnectionTds.AttemptOneLogin(ServerInfo serverInfo, String newPassword, Boolean ignoreSniOpenTimeout, TimeoutTimer timeout, SqlConnection owningObject) ..... -
Cause
Antivirus or Firewall is blocking the connection to SQL Server. -
Resolution
Per user report, the issue is caused by a setting in the 'Symantec Endpoint Protection' antivirus.
Go to 'Symantec Endpoint Protection' settings | then go to "Network Threat Protection" | "Unmatched IP Traffic Settings" section | choose "Allow IP traffic" (old setting was "Allow only application traffic". Restart Toad and re-test the issue.
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