Hiren Vora, I've corrected the model to sale.order.line in the python script (in bold now above), but the same error.

Maniganda, ok, I've changed the xpath expression into

<xpath
                    expr="//field[@name='product_id']" position="after">
                    <field name="Number_Pages"/>
                </xpath>

The detailed error message is:

'View error', u"Can't find field 'Number_Pages' in the following view parts composing the view of object model 'sale.order':\n * sale.order.form.inherit\n\nEither you wrongly customized this view, or some modules bringing those views are not compatible with your current data model")
2014-07-15 14:03:59,204 8094 ERROR test_2 openerp.tools.convert: Parse error in /home/wouter/odoo-dev/custom-modules/order_printing/order_printing.xml:4:
<record model="ir.ui.view" id="order_printing">
            <field name="name">sale.order.form.inherit</field>
            <field name="model">sale.order</field>
            <field name="inherit_id" ref="sale.view_order_form"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='product_id']" position="after">
                    <field name="Number_Pages"/>
                </xpath>
            </field>
          </record>
Traceback (most recent call last):
  File "/opt/odoo/odoo/openerp/tools/convert.py", line 852, in parse
    self._tags[rec.tag](self.cr, rec, n)
  File "/opt/odoo/odoo/openerp/tools/convert.py", line 819, in _tag_record
    id = self.pool.get('ir.model.data')._update(cr, self.uid, rec_model, self.module, res, rec_id or False, not self.isnoupdate(data_node), noupdate=self.isnoupdate(data_node), mode=self.mode, context=rec_context )

Hi Wouter,

Now as you have inherited proper model, try the xpath expression that you have tried earlier,  I have made one change in this - added the field name of order_line
  <xpath  expr="/form/sheet/notebook/page/field[@name='order_line']/form/group/group/field[@name='product_id']" position="after">

because If you look at the error it tries to find the field "Number_pages" under sale.order, which is not there, so do the way you did it earlier.

Try this one

<record model="ir.ui.view" id="view_order_form_inherit2">

<field name="name">sale.order.form.inherit2</field>

<field name="model">sale.order</field>

<field name="inherit_id" ref="sale.view_order_form"/>

<field name="arch" type="xml">

<xpath expr="//label[@for='analytic_tag_ids']" position="before">

<label for="page_number"/>

<div>

<field name="page_number" />

</div>

</xpath>

</field>

</record>

Hi

Try this code :

            <record model="ir.ui.view" id="order_printing">
            <field name="name">sale.order.form</field>
            <field name="model">sale.order</field>
            <field name="inherit_id" ref="sale.view_order_form"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='order_line']/tree/group/group/field[@name='product_id']" position="after">
                  <field name="Number_Pages"/>
                </xpath>
            </field>
          </record>

@Wouter- The xpath which you have written

<xpath
                    expr="/form/sheet/notebook/page/field/form/group/group/field[@name='product_id']" position="after">
                    <field name="Number_Pages"/>
   </xpath>

will try to find the field "product_id" in sale_order_line object, but you have created the field 'Number_Pages' in sale_order object, this will give an invalid xml architecture error.

either you can create the field in sale_order _line and use the xpath which you have already written in your code or you can write a xpath sale_order object directly like

<xpath
                    expr="//field[@name='name']" position="after">
                    <field name="Number_Pages"/>
   </xpath>

Would it not be easier to not use the Xpath, but instead rely on OpenERP xml-inheritance position for this? So:

<field name="product_id" position="after">

    <field name="Number_Pages"/>

</field>

Or does this not work in your case?

By the way, are you sure you have the right inheritance structure (you don't have the _name-tag in your object).