MIRO - Balance not equal to zero message, with Material Ledger active

Hi,

I created a standard purchase order - ME21N - for a material with the total value of 3000 MXN (500 pieces x 6 MXN/piece - price taken from purchase info record).

Then I posted a goods receipt of the whole amount of 500 pieces - MIGO.

Next I tried to post an invoice in t-code MIRO in reference to the purchase order, however with the invoice amount of 4000 MXN, i.e. higher compared to PO amount by 1000 MXN. I enterred the amount of 4000 MXN in the header and then I corrected the item amount from 3000 MXN to 4000 MXN which gave me the balance of 0 MXN and green light.

Unfortunately this invoice cannot be posted. I get the following green message:

"Balance is not equal to zero: 1.000,00 MXN

Message no. M8186

Diagnosis

You cannot post the document as the balance is 1.000,00 MXN.

Procedure:

Check the gross invoice amount, the tax amount, the amounts in the items selected and any unplanned delivery costs in the document header. The items selected on the item list may not be the same as those in the invoice."

This message doesn't make any sense for me because the balance is equal to zero, as the green light in the upper right corner and the figure 0 MXN show.

Could you please give me some advices, where the problem is? I would like to add that the material ledger is active.

I will be very grateful for your help / advices.

Regards,

Robert