Re: NCO 3 An unhandled microsoft .net framework exception occurred in w3wp.exe

Well, you shall avoid calling this section more than once:

SAPConfig sapCfg = new SAPConfig();
try
{    try    {        RfcDestinationManager.RegisterDestinationConfiguration(sapCfg);    }    catch { }    SapRfcDestination = RfcDestinationManager.GetDestination(Destination);

Rather use the other variant of GetDestination():

var par = new RfcConfigParameters();
//config par here
....
var dest = RfcDestinationManager.GetDestination(par);

or call the RfcDestinationManager.RegisterDestinationConfiguration(sapCfg); only once when your application starts. Yet SapRfcDestination = RfcDestinationManager.GetDestination(Destination); can be called as many times you want.