Geoprocessor gp = new Geoprocessor();
gp.OverwriteOutput = true;

ITrackCancel trac = new ESRI.ArcGIS.Display.CancelTracker();

string input = File.ReadAllText(fdlFile, Encoding.UTF8);
QuickImport import = new QuickImport();
import.Input = input.Replace("FDLVERSION1,", ""); ;
//import.Output = "C:/temp/wfs.gdb";

Type factoryType = Type.GetTypeFromProgID("esriDataSourcesGDB.FileGDBWorkspaceFactory");
IWorkspaceFactory workspaceFactory = (IWorkspaceFactory)Activator.CreateInstance(factoryType);
IWorkspaceName wsn=workspaceFactory.Create("C:/temp", "wfs.gdb", null, 0);
import.Output = wsn;

try
{
    // error occurs here:
    object resi = gp.Execute(import, trac);
}
catch (Exception ex)
{}