The supplier does not have any VAT attached to them yet the purchase invoice does.
The main cause of this problem is when the Supplier’s tax rate has been changed from one percentage to another in Supplier Entry after one of its timesheets has already been submitted. This causes timesheets which have already been submitted to still carry the previous Supplier tax rate not the updated tax rate.
When changing tax rates for a Supplier, you must check that all timesheets submitted before this change, are updated to the new tax rate. Submitted timesheets will not update automatically to the new tax rate so you will need to update them yourself. You can do this by selecting the timesheet and then selecting the current tax type and click Update (make sure you click the Show Complex Rates button to be able to view this):
If the Purchase invoice has already been created then you can do the same as above in Invoice/Remittance Edit where you will see the timesheet for that invoice. Click the pencil and update the timesheet just like in the image above. You will also need to recreate the invoice document to reflect the changes.
If the Purchase Invoice has already been delivered to the Supplier with the incorrect tax rate then the purchase invoice will need to be credited.