iOS OTA updates don't work if you're Jailbroken
If you're Jailbroken and trying to get iOS 5 beta 4 via over-the-air (OTA) update, you just might be out of luck according to iPhone Dev-Team member MuscleNeard:
The 5.0b4 OTA update won't work on JB devices due to an explicit check of /Applications..almost like a present from Apple
they check to make sure /Applications is a real directory, which it isn't in a stashed jailbreak (not sure how unionfs would act)
Never underestimate the resourcefulness of the Jailbreak community, but if you want to try OTA now you'll likely have to restore to iOS 5 beta stock before proceeding.