problems with url change in the webform

Can some one plzz help me with this
I have an issue, I have a webpage which is like a booking engine, it gives  you start date and end date for your journey and a promotioncode field by clicking enter the page gets directed to another webform, now the url of the page with promotion code is like shown below
http://localhost:89/bidding/booking?start=16/05/2010&end=23/05/2010&people=2&discount=ejo20--valid code


http://localhost:89/bidding/booking?start=16/05/2010&end=23/05/2010&people=2&discount=ABC009--Invalid code
 




if I change the Url here and give some other invalid promotion code then it doesnot give me any error, where as in the first webform if I give the wrong promotion code it shows me error there itself and doesnot allow me to next webform.
What do I have to look into this?webform 1 or 2 and which part of the code...plzzzz

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