The line with self.pool.get('product.bom_ids') doesn't look good.

it should be like self.pool.get(model.name), so self.pool.get('product.bom'), if product.bom is the name of the class/object for the Bill of Material.

Further, on which line does the error happen? It might be noted in the log-file.

I managed to solve it myself :)

It was actually very easy without doing any code. Since a order.line contains the actual product, and a product has a reference to its boms, it looks like this: (show_bom and show_discounts are custom fields I added by inheriting "sale.order")

<section>
  <para style="terp_default_1">[[repeatIn(o.order_line,'line')]]</para>
  <blockTable colWidths="250.0,80.0,70.0,50.0,85.0" style="Table5">
    <tr>
      <td>
        <para style="terp_default_9"><b>[[ format(line.name) ]]</b></para>
        <para style="terp_default_9">[[ format(line.product_id.description) or removeParentNode('para') ]]</para>
        <section>
            <para style="terp_default_9">[[ o.show_bom and repeatIn(line.product_id.bom_ids,'bom') ]]</para>
            <para style="terp_default_9"> </para>
            <para style="terp_default_9">Stückliste: [[ format(bom.name) ]]</para>
            <section>
                <para style="terp_default_9">[[ repeatIn(bom.bom_lines,'bomline') ]]</para>
                <blockTable style="Table3" colWidths="220.0,60.0,60.0">
                    <tr>
                        <td>[[ format(bomline.product_id.name) ]]</td>
                        <td>[[ bomline.product_qty ]]</td>
                        <td>[[ o.show_bom and formatLang(bomline.product_id.list_price, digits=get_digits(dp='Product Price')) ]]</td>
                    </tr>
                </blockTable>
            </section>
        </section>
      </td>
      <td>
        <para style="terp_default_Right_9">[[ formatLang(line.product_uos and line.product_uos_qty or line.product_uom_qty) ]] [[ line.product_uos and line.product_uos.name or line.product_uom.name ]]</para>
      </td>
      <td>
        <para style="terp_default_Right_9">[[ not o.show_discounts and formatLang(line.price_unit * (1 - line.discount / 100) , digits=get_digits(dp='Product Price')) or formatLang(line.price_unit , digits=get_digits(dp='Product Price'))]]</para>
      </td>
      <td>
        <para style="terp_default_Centre_9">[[ o.show_discounts and formatLang(line.discount, digits=get_digits(dp='Discount')) or '']]</para>
      </td>
      <td>
        <para style="terp_default_Right_9">[[ formatLang(line.price_subtotal, digits=get_digits(dp='Account'), currency_obj=o.pricelist_id.currency_id) ]] </para>
      </td>
    </tr>
  </blockTable>
</section>