Problems upgrading iPhone 4

Hi

I have an iphone 4 running 4.3.2 (8H7) with baseband 04.10.01 using a GEVEY sim tray.

I want to upgrade to IOS 5.

I have preserved my IOS 5.0.1 baseband using Redsn0w_mac_0.9.12b1. Put my phone into DFU mode and tried to update in iTunes.

But I receive a 'The iPhone could not be restored. This device isn't eligible for the requested build'

I have adapted my HOST file and tried using Tiny Umbrella yet still no luck.

Does anyone else have any ideas???