When an XML Web service client adds a SOAP header to an XML Web service method call with the SoapHeader.MustUnderstand property set to true, the XML Web service method must set the SoapHeader.DidUnderstand property to true; otherwise, a System.Web.Services.Protocols.SoapHeaderException is thrown back to the XML Web service client by ASP.NET.

Although both the SoapHeader.EncodedMustUnderstand and SoapHeader.MustUnderstand properties can be used to set the value of the mustUnderstand attribute within the SOAP header, the SoapHeader.MustUnderstand property allows you to set the attribute using a Boolean value.

For details on adding SOAP headers to clients, see [<topic://cpconusingsoapheaders>].