'23/02/2011 12:34:56' is not valid date and time

In my code I am facing a problem. Example code:

var 
    d1: tdatetime
begin
    d1 := strtodatetime('23/02/2011 12:34:56');
end; 

but it's giving the error:

'23/02/2011 12:34:56' is not valid date and time

What's wrong with what I am doing?