ifup fails but iwconfig and dhclient works?

[pinniped <cirilo_bernardo@yahoo.com>]

It sounds like your network script is running while the wireless driver hasn't finished setting up.  I have an EPX form computer out in the field and it's got an rt2570 in it. Because of the peculiar way that machine operates, I use pre-up/post-down to load and unload the driver; the driver itself is blacklisted so it's not automatically loaded at boot.  Of course the 'pre-up' loads the driver as the network script is running.  I have never had problems with that machine - maybe you can try the same and see what happens? I must admit that if it works it's a voodoo solution - you still wouldn't have identified the actual problem.