your date elements are using the dd/mm/yyyy format, but the spry validation is exprecting the mm/dd/yyyy fprmat.
change:
var Booking_Enquiry_group_Dates_From_Spry = new Spry.Widget.ValidationTextField("Booking_Enquiry_group_Dates_From_Spry", "date", { format:'mm/dd/yyyy' , validateOn:["blur"]});
var Booking_Enquiry_group_Dates_To_Spry = new Spry.Widget.ValidationTextField("Booking_Enquiry_group_Dates_To_Spry", "date", { format:'mm/dd/yyyy' , validateOn:["blur"]});
to:
var Booking_Enquiry_group_Dates_From_Spry = new Spry.Widget.ValidationTextField("Booking_Enquiry_group_Dates_From_Spry", "date", { format:'dd/mm/yyyy' , validateOn:["blur"]});
var Booking_Enquiry_group_Dates_To_Spry = new Spry.Widget.ValidationTextField("Booking_Enquiry_group_Dates_To_Spry", "date", { format:'dd/mm/yyyy' , validateOn:["blur"]});