Good question. I ran up against an issue in data before where it was not actaully a valid numeric value, but passed the isnumeric test and broke the process upon insert. The only thing I would add beyond the difference in formating between countries is that you could just have some plain bad data like the following that would pass the isnumeric test

DECLARE @PrincipalAmount VARCHAR(15)SET @PrincipalAmount = '7,0,0,,,0.0,0,,,'

SELECT ISNUMERIC(@PrincipalAmount)

Regards,

Toby