what kind of this error

Instead of adding hVp3D to 'this' add hVp3D to grid as gridName.Childrens.Add(hVp3D);

I think while adding the child elements it is showing error. Check this link, https://stackoverflow.com/questions/12609724/content-of-a-contentcontrol-must-be-a-single-element-exception

I think while adding the child elements it is showing error. Check this link, https://stackoverflow.com/questions/12609724/content-of-a-contentcontrol-must-be-a-single-element-exception