Don't rely on the IDENTITY column to drive the sequence. IDENTITY is
only supposed to be an arbitrary key. EntryTime should be a better way
to do it:

UPDATE tblProfileTemp
SET gross =
(SELECT T0.gross +
((T2.gross - T0.gross) *
((tblProfileTemp.runtime-T0.runtime)/(T2.runtime-T0.runtime)))
FROM tblProfileTemp AS T0,
tblProfileTemp AS T2
WHERE T0.entrytime =
(SELECT MAX(entrytime)
FROM tblProfileTemp AS T
WHERE entrytime < tblProfileTemp.entrytime
AND gross IS NOT NULL)
AND T2.entrytime =
(SELECT MIN(entrytime)
FROM tblProfileTemp AS T
WHERE entrytime > tblProfileTemp.entrytime
AND gross IS NOT NULL))
WHERE gross IS NULL

Thanks for posting the DDL and sample. It helped.

--
David Portas
SQL Server MVP
--