How to read and process xml data from stored procedure in sql server?
You don't need to SET the XMLRESULT. 

You should pass it in as an OUTPUT parameter.

https://technet.microsoft.com/en-us/library/ms187004(v=sql.105).aspx

DECLARE @XMLRESULT xml;
EXEC usp_ReportResults @query = '759,905,1048,170,725,80129', @ReportName ='GenRepot', @XMLResult = @XMLRESULT OUTPUT;


You can then use the @XMLRESULT parameter, which has been populated with the result of the Stored Procedure.

INSERT INTO dbo.my_table(xml_field)
SELECT @XMLRESULT;