Вызов фильтра производится так
%catalog search('%category_id%', 'filtr_po_tovaram cenovye_svojstva', 'proizvoditel_search)%
В шаблон /templates/pro-busy/tpls/catalog/proizvoditel_search.tpl
$FORMS['search_block_line_relation'] = <<<END
<dl class="selectContainer">
<dt><label for="itemType">%title%:</label></dt>
<dd>
<select name="fields_filter[%name%]" size="1" class="selectbox" id="itemType">
<option value="">Все</option>
%data doSelection('search_filter_data_usel', 'search_filter_usel', %type-id%,id,asc)%
</select>
</dd>
</dl>
<!-- <label>%title%:</label>
<select name="fields_filter[%name%]" class="textinputs" onchange="this.form.submit()">
<option value="">Все</option>
%data doSelection('search_filter_data_usel', 'search_filter_usel', %type-id%,id,asc)%
</select> -->
END;
Вставил %data doSelection('search_filter_data_usel', 'search_filter_usel', %type-id%,id,asc)%
И вот что получаю
<udata generation-time="0.0"><error>You don't have permissions to call protocol "usel://" via HTTP</error></udata>