DECLARE @Foo TABLE 
(
	Record INT,
	EmployeeId INT,
	DOS INT,
	SupervisorId INT,
	ProblemCode CHAR(3)
)
INSERT @Foo VALUES
(1, 1, 20120101, 10, 'f25'),
(2, 1, 20120101, 10, 'f10'),
(3, 1, 20120101, 10, 'f01'),
(4, 1, 20120101, 26, 'f01'),
(5, 1, 20120101, 26, 'f55')

SELECT 
	*,
	ROW_NUMBER() OVER 
	(
		PARTITION BY 
			EmployeeID, 
			DOS, 
			CASE 
				WHEN 
				(
					SupervisorID <> PreviousSupervisorID 
					AND ProblemCode = PreviousProblemCode
				)
				THEN
					PreviousSupervisorID
				ELSE
					SupervisorID
			END
		ORDER BY
			Record
	) AS RowNum
FROM
(
	SELECT 
		*, 
		LAG(SupervisorID, 1, NULL) OVER (ORDER BY Record) AS PreviousSupervisorID,
		LAG(ProblemCode, 1, NULL) OVER (ORDER BY Record) AS PreviousProblemCode
	FROM @foo
) AS A