Fillet radii, tricky creation

Hello,

I am creating a fillet radius in the place indicated in the picture, but all the time I try it just does it but in the simmetric part. I attach a sample of the piece where I'm trying to put the fillet.

Please, would you mind giving to me an hand and teach how to do it, thank you.

http://www.mediafire.com/download.php?6i0b58kzhapvc6r

Kind regards,

Antonio

SolidworksParts And Features