Thanks you for the follow up solution. Sorry I could not have been more helpful.

>My friend explain, what happen:
>
>If I have function, which makes Inserts, Updates or Deletes on MyTable, I cannot call this function with 'select package.MyFunction() from dual', because, same call can be 'select package.MyFunction() from MyTable' too, and Oracle doesn't know (if function modified MyTable), what return.
>
>It works, if is function calling from PL/SQL:
>declare
> promX NUMBER;
>begin
> promX := package.MyFunction();
>end;
>/
>
>Pavel