NAV 2013 error

Help ! We keep getting this error message when testing in NAV 2013 I am trying to invoice off a purchase order.

‘Vendor invoice no. must have a value in purchase header: Document type= Order, No.= POR000002. It cannot be zero or empty’

We started to build this company from scratch and are currently in the ‘testing’ phase so we have built the dimensions etc… we have set our No series and I have checked them and they all seem correct. We have purchase orders with a number series of POR000000 - POR999999 and the tick box is for Default. Cannot think or what it is!

Turn off “Ext. Doc. No. Mandatory” in “Purchase & Payables Setup”. Or fill in the required information on the purchase order.

There is the field in Purchase invoice “Vendor invoice No.” Fill this filed.

this field use for:Specifies the number that the vendor uses for the invoice you are creating in this purchase invoice header.

if solved than tik this subject as solve.

Regards
Suraj

Its not that that is causing the issue. I have completed that filed and even tried the above suggestion of turning that ‘ext. doc. man’ off.

its something to do with the order number field cannot be zero or empty but the system auto fills the Purchase order number and there is a POR number in there.

there is nothing behind the scenes that I need to do ??