Are you sure that @s1_count is actualy declared as integer? What result would you get if you run from Query Analyzer?

SELECT count(fib_s1) from dsiweb.dbo.s2p2_results
		  where fib_s1>0 and inst_type='S'
		  and fib_lot = @fib_lot

>I tried your suggestion... same result.
>
>Arithmetic overflow error converting numeric to data type numeric.