XmlWriter.WriteElementString Method (String, String)
Writes an element with the specified local name and value.
Assemblies: System.Xml (in System.Xml.dll)
System.Xml.ReaderWriter (in System.Xml.ReaderWriter.dll)
The localName value is a null reference (Nothing in Visual Basic) or an empty string.
The parameter values are not valid.
There is a character in the buffer that is a valid XML character but is not valid for the output encoding. For example, if the output encoding is ASCII, you should only use characters from the range of 0 to 127 for element and attribute names. The invalid character might be in the argument of this method or in an argument of previous methods that were writing to the buffer. Such characters are escaped by character entity references when possible (for example, in text nodes or attribute values). However, the character entity reference is not allowed in element and attribute names, comments, processing instructions, or CDATA sections.
An XmlWriter method was called before a previous asynchronous operation finished. In this case, InvalidOperationException is thrown with the message “An asynchronous operation is already in progress.”