help with downgrade 3gs ios 5beta 5 to ios 4.3.5

i just got my iphone 3gs i updated to ios 5 beta 5 its buggy so i been tried to restore my phone back to 4.3.5 when i do i keep getting error 1015 and its stuck in recovery mode tried to use tiny umbrella and kick i out of recovery but it goes back into it i tried ireb that dont work either can someone please help thanks
i forgot when i tried to downgrade to 4.3.5 i use itunes 10.4
my baseband is 05.16.05
1. no SHSH file on the iphone.
2. Cannot kick the phone out from the recovery mode.