the x and y variables are created when you use an image input type for a submit button:
<input type="image" name="Search" id="Search" value="Search" alt="Search" src="WA_DataAssist/images/Nautica/Modular_search.gif" />
In some browsers, the value of image input type is not passed, instead the x and y coordinates of where the mouse clicked the image are passed.
When an image input type is used, the trigger for the search will be set to use the $_GET['Search_x'] variable so that the search will work correctly in all browsers.
You will also need to modify the search server behaviors trigger.
On the results page, open the bindings panel. Click the plus button and select Form Data. Inthe form data dialog, click the folder icon and select the search form.
this will bring in the search form elements to the results page bindings panel.
Now open the server behaviors panel and Double Click the Data Assist Search behavior.
click the lightning bolt next to Trigger and select the S_ItemCatID form element so the search will be triggered by the select list.
Now on the search page, change the select list tag:
<select id="S_ItemCatID" name="S_ItemCatID">
<select id="S_ItemCatID" name="S_ItemCatID" onchange="documet.WADASearchForm.submit();">