Error string has not valid datetime?

Question

Hi...

 in reportviewer i'm goning to send startdate and end date of type string(yyyy/mm/dd format) to stored procedure,
 In table, Starttime and endtime are DATETIME datatype,IN table datetime in dd/mm/yyyy format.

 when i click buton report show An error has occurred during report processing.String was not recognized as a valid DateTime.? Error
Please help me 
thanks in advance.............