While attempting to login C#, Soap API, enterprise wsdl. I am getting INVALID_LOGIN: Invalid username, password, security token; or user locked out.error. I will be grateful for any assistance in resolving this error.
My Code is 
SoapClient loginClient = new SoapClient("Soap");
            string sfdcUserName = "abc@gmail.com";
            string sfdcPassword = "Password";
            string sfdcToken = "LegAguRb2CzEifnoiPNcVT5UE";
            //Login
            LoginResult result = loginClient.login(null, sfdcUserName, string.Concat(sfdcPassword,sfdcToken));
            //Read the information
            mSessionId = result.sessionId;
            mServerURL = result.serverUrl;

My task is to migrate knowledge articles from pre-prod sandbox to production. The knowledge articles predominantly FAQ are created in the pre-prod sandbox and are to be migrated to production. What is the best way to do this?

Attempting to login C#, Soap API, enterprise wsdl. I am getting INVALID_LOGIN: Invalid username, password, security token; or user locked out.error. 
My Code is 
SoapClient loginClient = new SoapClient("Soap");
            string sfdcUserName = "abc@gmail.com";
            string sfdcPassword = "Password";
            string sfdcToken = "LegAguRb2CzEifnoiPNcVT5UE";
            //Login
            LoginResult result = loginClient.login(null, sfdcUserName, string.Concat(sfdcPassword,sfdcToken));
            //Read the information
            mSessionId = result.sessionId;
            mServerURL = result.serverUrl;