How to update data on particular invoice field.

Dear Experts,

We want update data on invoice form level,So while updated Data on particular invoice number field throw Examine Diagnostic Tool we face following Error.

APP-FND-00560

Remember invoice is already validated and paid therefore invoice number field is Grey.

Here My Question is:

• How this error is appear on that particular invoice
• Is there any other alternative workaround to be update this particular grey field.

Regards

Ayaz Iqbal

Note:You will found issue related further information on attached file.