MWVS re-calculation with change in tax code on Invoice tab screen in PO

Hi! We have previously set up a pricing procedure with an access sequence that has 4 sequences. We will concentrate on the first two in this case. The first one is using fields KOMK-LAND1 (destination country) and KOMK-MWSKZ (tax code). The second one is using fields KOMK-LAND1 (destination country), KOMP-TAXIM (tax ind from material), KOMP-TAXIW (tax ind from plant) and KOMP-TAXIL(import). We have condition records created for the above 2 condition tables.

Example of condition records:

Condition table 1 810 Taxes: Destination Country/Tax Code

NZ, P0 -> 0%, P0

NZ, P1 -> 12.5%, P1

Condition table 2 86 Taxes: Material, Plant and Origin

NZ, 1, 1, 0 -> 12.5%, P1

Now, when we create a PO for a local vendor, the system picks up the tax code P1 from condition table 2. Looking at the pricing analysis, it outputs a message 'Access not made (initialized field)' with exclamation mark on the tax code field for condiiton 1 and found the condition record for condition 2 which is correct since the system will then default the tax code found from the condition record.

Now, if we change the tax code on the Invoice tab from P1 to P0 and update pricing on the condition screen, the tax still remains as P1 even though we have a condition record created for condition 1. Again, looking at the pricing analysis, it outputs a message 'Access not made (initialized field)' with exclamation mark on the tax code field for condition 1 and found the condition record for condition 2.

Any idea why I am getting the 'Access not made' message? Is it actually possible to re-determine tax code based on the tax code that is already determined earlier on the Invoice tab screen? Also, I noticed that the tax code is at header level, is that the reason why we are getting the above message?

Reason why we have configured the system this way is that the users want the system to determine and calculate tax based on the material, plant and origin but there are occasion where they want to be able to change the tax code and have the tax amount re-calculated. But I am not sure whether we can change the tax code on the Invoice tab screen and get the system to go through the pricing calculation again to re-determine the new tax amount (and same tax code) picking the first condition in this case. Does not quite make sense to me but I just want to double check.

Appreciate any help on this.

Thanks!

SF