Am not saying I *like* this (due to having to 'hook' the IsNaN function to the equation, doesn't appear to allow it to stand alone) but it works....

=Iif((Fields!field1.Value / Fields!field2.Value).IsNaN(Fields!field1.Value / Fields!field2.Value), 0, Fields!field1.Value / Fields!field2.Value)

so psuedo-code... if A / B is NaN then 0 else A / B

HTH,