Dynamic Date Parameter In Report Manager

Hi all,

I was wondering if there's a way to override the default date parameter of a report to a dynamic value such as Today(), Now(), DateAdd(),... through Report Manager.

I know this can be done in Report Designer, but never been successful when I try to change the date parameter value in Report Manager.

I've tried to change the date parameter value by clicking on the Override Default button in the report's properties page from Report Manager, error like the one below will be shown after I entered Now() in the Default Value field and clicked Apply:
The value provided for the report parameter 'StartDate' is not valid for its type. (rsReportParameterTypeMismatch)

Thanks in advance.