Hi,
This is because, you defined domain or attributes for one2many field inside the tree view
INCORRECT :
<page string="Purchase Request">
<field name="order_line"> ----------- (one2many field)
<tree string="Purchase Req Order Lines" editable="bottom">
<field name="part_name" attrs="{'readonly':[('state','not in',('draft',))]}"/>
<field name="price_unit" attrs="{'readonly':[('state','not in',('draft',))]}"/>
<field name="sub_total" attrs="{'readonly':[('state','not in',('draft',))]}" />
</tree>
</field>
</page>
Correct :
<page string="Purchase Request">
<field name="order_line" attrs="{'readonly':[('state','not in',('draft',))]}"> ----------- (one2many field)
<tree string="Purchase Req Order Lines" editable="bottom">
<field name="part_name" />
<field name="price_unit"/>
<field name="sub_total" />
</tree>
</field>
</page>
- state field is present only in main class. Hope this may solve your problem