The autoinc fields are read-only by design.

>After have tried some solutions, I tried autoincremental integer field and it showed to work very well
>
>I simulated 2 forms adding data to a table simultanealy and
>very quickly using the form timer.
>
>It seems to work fine, and there is no duplicate code.
>
>The problem is that costumer can not edit the invoice number
>because this field seems to be read only
>