Filter Search (just like on webassist products page)

for the search form:

1) the WADbSearch1 need to have a value:

<input name="WADbSearch1" type="hidden" value="search">

2) the option element cannot have a name:
<option name="WADbSearch1" value="<?php echo $row_rsCategories['CategoryID']?>"<?php if (!(strcmp($row_rsCategories['CategoryID'], $row_allProducts['ProductCategoryID']))) {echo "selected=\"selected\"";} ?>><?php echo $row_rsCategories['CategoryName']?></option>

remove the name attribute from the option code

for the sort form:

the page name should not be part of the select list option, only the name of the column to sort:
<option value="ProductSKU" >SKU</option>

to pass the page=manage-products variable in a form that uses the get method, you need to use a hidden element:

<input name="page" type="hidden" value="manage-products">