Also your select statement will normally return a number of rows before it actually falls over so you could use that as a point in the DB to start looking for bad data

e.g

DECLARE @Tmp TABLE

(COl1 VARCHAR(100))

INSERT INTO @Tmp

SELECT '1' UNION ALL

SELECT '1111111111111111111111'

SELECT CAST(col1 as decimal(12,7))

FROM @Tmp

This fails but it also return one row, so I know that it's after the first row etc...