Start Editing Return Unspecified error (Exception from HRESULT: 0x80004005 (E_FAIL))

I'm using IEngineEditor.StartEditing method to start an edit session on SDE Workspace. My workspace is having a right value because I have no problem to get a feature class using it. I'm not sure where I did wrong, or what causing this error. Please help.

 IPropertySet propertySet = new PropertySetClass();
 propertySet.SetProperty("SERVER", MyServer);
 propertySet.SetProperty("INSTANCE", MyInstance);
 propertySet.SetProperty("DATABASE", MyDatabase);
 propertySet.SetProperty("USER", MyUsername);
 propertySet.SetProperty("PASSWORD", MyPassword);
 propertySet.SetProperty("VERSION", MyVersion);

 Type factoryType = Type.GetTypeFromProgID("esriDataSourcesGDB.SdeWorkspaceFactory");
 IWorkspaceFactory workspaceFactory = (IWorkspaceFactory)Activator.CreateInstance(factoryType);

 IWorkspace workspace = workspaceFactory.Open(propertySet, 0);

 IFeatureWorkspace pFeatureWorkspace = workSpace as IFeatureWorkspace;
 IFeatureClass pFeatureClass = pFeatureWorkspace.OpenFeatureClass("MyFeatureClassName"); //I can get this feature class. This was for later use
 IMap pMap = mapControl.Map;

 engineEditor.StartEditing(workSpace, pMap);