Well both of them work for me the only difference is that with out the a option the dialog will appear in the center of the mirc program and with the a it will appear on the center of the log window.
Which was exactly the problem, because if it appeared in the center of mIRC it was useless... as the log window was completely covered.
The a will work with the active window (the log in this case)
Exactly the point.
But good to know that it work's for you now them.
and hopefully anyone else that ever wonders, can find it here now too.