I have an error while get orderdata using Dateinterval.

Economic.Api.Exceptions.SchemaException(E00500): The 'http://e-conomic.com:first' element is invalid - The value '2011-03-2100:00:00' is invalid according to its datatype 'http://www.w3.org/2001/XMLSchema:dateTime' - The string '2011-03-2100:00:00' is not a valid XsdDateTime value. {id=1442040043}


I used this following coding


$i = date('2011-03-21\00:00:00');
$v = date('2011-03-26\00:00:00');


$orderHandle23=$client->Order_FindByDateInterval(array('first'=>$i ,'last'=>$v))->Order_FindByDateIntervalResult;