As you haven't supplied the actual filter you are using I can only guess at the answer.
I suspect that you are not putting quote marks around the date so if you have something like
datum > 07/26/2004
it is trying to divide 7 by 26 and then by 2004 which will appear to be an Arithmetic expression.
You should have something like
datum > '07/26/2004'
However, if your DateSeparator is defined as -
then you need to do something like
datum > '07-26-2004'
Andrew
Hampshire, UK