Problem assigning a taskID to a message in a MessageAssignment shape

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taskID = System.Guid.NewGuid();

RequestCheckMessage(Microsoft.BizTalk.Hws.HwsPromotedProperties.TaskID) = taskID.ToString();

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Even if I just took this code from an example I found online, it does not work: my action instance remains suspended after I receive this exception:

<<Microsoft.XLANGs.RuntimeTypes.XPathUpdateException: A failure occurred while evaluating the property Microsoft.BizTalk.Hws.HwsPromotedProperties.TaskID against the message part data. The message part data does not contain at least one of the nodes specified by the XPath expression (listed below) that corresponds to the property. The cause for this error may be that the message part data has not been initialized or that the message part data does not conform to the message part schema. Ensure that the message part data is initialized correctly. XPath expression: /*[local-name()=’HwsMessage’ and namespace-uri()=’http://tempuri.org/Hws_RequestCheck’%5D/*%5Blocal-name()=’HwsSection&#8217; and namespace-uri()=”]/*[local-name()=’TaskID’ and namespace-uri()=”]…>> in Microsoft.XLANGs.Core.XSDPart.SetPayloadProperty(PropertyDefinition pd, Object val)…

 Please, can you help me to get through this error?

Thank you in advance,

Emiliano.