Attempt To Catch Error Using @@ERROR In SQL 2000 Is Failing

We have a stored procedure that calculates the floor nr for users at our company campus using their office location. The calculation is done by a function that returns an integer. Unfortunately, not all users enter their information correctly so the function sometimes raises an error. Below is the code of that stored procedure.



UPDATE PERSONS

SET FLOORNR = dbo.FloorNR(OFFICELOCATION)

WHERE OFFICELOCATION IS NOT NULL



IF(@@ERROR <> 0 OR @@ROWCOUNT = 0)

BEGIN

RAISERROR ('Failed to calculate the floor number', 16, 1 ) with nowait

END



However, when the function dbo.FloorNR fails, it doesn't raise our error, but it seems to raise the error that comes from dbo.FloorNR.



How can we catch errors that come from dbo.FloorNr so that we can raise our own error? Our company still uses SQL 2000, so we cannot use the SQL 2005 try/catch option.