NetOffice - for professional COM Addin developers

Hi everybody,
I am trying to delete existing custom document properties from word documents... unfortunatly I am stuck with this...

public void DeleteAllProps(string SCurrentDocs)
{
var VWordApp = new NetOffice.WordApi.Application();
var VDoc = VWordApp.Documents.Open(SCurrentDocs);
var VCustomDocProp = (DocumentProperties)VDoc.CustomDocumentProperties;

foreach (var VProp in VCustomDocProp)
{
VProp.Delete();
}

if (VDoc != null)
{
VDoc.Save();
VDoc.Close();
VDoc = null;
}
if (VWordApp != null)
{
VWordApp.Quit();
VWordApp.Dispose();
VWordApp = null;
}
}


After saving the Document the custom document properties are still existing. Reading the properties in another Method was super easy...
Does anyone has a suggestion how to solve this problem?
Thank you!