InwiseWebServices.InwiseWebServices ws = new InwiseWebServices.InwiseWebServices();
//fill the security header
InwiseWebServices.SecHeader header = new InwiseWebServices.SecHeader();
header.username = "username";
header.pass = "myPassword";
ws.SecHeaderValue = header;//set credentials
string sessionToken = ws.Login();
//now I can use the new header
ws.SecHeaderValue = null;//clear the old header if you want
//create the new header
InwiseWebServices.AuthIdentifier sessionHeader = new InwiseWebServices.AuthIdentifier();
//set it's value
sessionHeader.identifier = sessionToken;
//set the service with the new header
ws.AuthIdentifierValue = sessionHeader;
//now I can continue the normal activity