Stored Procedure parameters Date Type Crystal Reports String Type

Hi All

I had Created Crystal Report Based on Stored Procedure

In the Stored Procedure Parameters Start Date is Type DATE and End Date of Type DATE

I had Created Report on Start Date as String and End Date as String Types

While I am changing the Start Date and End Dates From String to DATE in the Command Prompt In Crystal Reports

it is Saying the Failed to Retrieve the data from the data Base

What is solution for that in order to change the Start data and End Date String data Types to DATE data type In Crystal Reports

Please Advise

Thanks

Krishna .