COMException (0x80004005) when accessing Interop.Word.XMLNode properties

In our Word VSTO application we have sometimes the problem that accessing the properties (e.g. BaseName) of an XmlNode throws an exception although the XmlNode reference itself is valid (i.e. not null). In some cases we also found out, that when setting a breakpoint on a line like

string baseName = myXmlNode.BaseName;

the first time watching the myXmlNode.BaseName displayes the exception and few seconds later the same property can be read without an exception.

The XmlNode has been created in the header/footer of the Word document.

Any idea how we can avoid or work around this problem

Thanks,
Joe