NAV 5.0 (SP1) EMP Portal - Search Web Part Issue 1

Hello All Experts,

According to the user manual I have created the Search Web Part for searching the Sales Order from the Sales Order List.
In that, Search Table - Sales Header.
And Search Fields -
1) No.
2) Name

If I am searching No. using *@SO* then I can get all related Sales Orders.

But when I am giving,
1) No
2) Name
3) Order Date

If I am searching No. using *@SO* then It gives me error,
"You have entered the Invalid Date. Refer the Online Help."

Same thing for Option type of field.

That means it gives more prioroity to Date, Option fields then Code or any thing else. I am not getting.

Please, help me urgently.
Thanks in Advance.