Hi, I had the same problem when I did a firmware update of my PB 903 from version 2.1.2 to 2.1.3. Before the update, my hidden wifi was working fine.
That's a bug in firmware 2.1.3 (hope it will be fixed in the next version - there were rumours that it might be shipping in july, but it looks like it will take much longer, my guess would be christmas
). Till then I'll be fine with my downgrade to 2.1.2 (the one with the fast display-driver).