Days Calculation - Error

Hi -

I have created this formula to calculate the number of days between the two dates. Bye the way, these two dates are stored as Strings.

Date ({CallLog.ClosedDate}) - Date ({CallLog.RecvdDate})

This formula seems to be working until I scroll through the first 3 pages of the report, then Crystal takes me back to the formula and gives me an error that says 'Bad Date Format String', it also highlights the first part of this formula.

Am I missing something?

Thanks for your help in advance.

G.