Product Advertising API Signed Requests, REST/QUERY issue

first thing i did i download this sample code : enter link description here2480

then i tried to copy the complete constructed URL and run it on a browser but i got an error : "Your request is missing required parameters. Required parameters include AssociateTag." , instead of returning an xml script

i think the error is that the c# code is missing the AssociateTag because there is'nt a place to add it in the sample code . thanks in advance