Wirelessly posted (Mozilla/5.0 (iPhone; CPU iPhone OS 5_0_1 like Mac OS X) AppleWebKit/534.46 (KHTML, like Gecko) Version/5.1 Mobile/9A405 Safari/7534.48.3)
Is your iPhone jailbroken? Tiny Umbrella is for that type situation. You might try to download & install the update on a computer that's not the main iTunes computer. For me, I use my laptop to DL and install updates, but restore after the update on my desktop, which IS the main iTunes location. Works well.
For some reason, I get an error message every time when using the desktop to update. Go figure.