access url problem parameter

I pass one parameter to my report .

it is ReportDate which is string .

http://webtest/reportserver?/VendorStat/HCV2005&rs:Command=Render&rc:Parameters=False&ReportDate=3/31/2005

I get this error message.

Default value or value provided for the report parameter 'ReportDate' is not a valid value. (rsInvalidReportParameter) Get Online Help

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I think there is sth wrong with ReportDate=3/31/2005

it should be "/" I tried "%2f", it is still wrong.

The error isn't complaining about the format of the date you specified, but rather the date itself. Your report is specifying a list of valid values for a ReportDate. In the RDL, you have provided either a static list, or a query that returns the set of possible values for a parameter. "3/31/2005" is not in that list.