Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, , >= or when the subquery is used as an expression.

ALTER PROCEDURE [dbo].[RmsUpdateRoAssignReAssign1]
(
@XMLAssignRo  AS XML
)
AS
BEGIN
	UPDATE RmsActivity 
				SET 
						RmsProcessorID = DocumentElement.AssignReAssignRo.value('(UserID)[1]', 'INT' ),
						LastUpdatedByID= DocumentElement.AssignReAssignRo.value('(UserID)[1]', 'INT' ),
						LastUpdatedDate=GETDATE()
						
				FROM	
						@XMLAssignRo.nodes('/DocumentElement/AssignReAssignRo') DocumentElement(AssignReAssignRo)
						INNER JOIN RmsUserSkillSet RS
						ON 
							 RS.RmsSkillSetTypeID =  
							 CASE 
								 WHEN DocumentElement.AssignReAssignRo.value('(Aging)[1]', 'INT' )< =20  THEN 1					
								 WHEN DocumentElement.AssignReAssignRo.value('(Aging)[1]', 'INT' ) BETWEEN 21 AND 30  THEN 2
								 WHEN DocumentElement.AssignReAssignRo.value('(Aging)[1]', 'INT' ) >=31 THEN 3							
							 END 
						INNER JOIN tblRoamingUsers RU
						ON RS.RoamingUserID=RU.RoamingUserID
						AND RU.UserID=DocumentElement.AssignReAssignRo.value('(UserID)[1]', 'INT' )
						INNER JOIN tblCampus C
						ON	C.CampusID=DocumentElement.AssignReAssignRo.value('(CampusID)[1]', 'INT' )
						AND RU.SchoolID=C.SchoolID
				WHERE
						RmsActivityID = DocumentElement.AssignReAssignRo.value('(ActivityID)[1]', 'INT' )
END		

(Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.)