No, downgrading the iOS is not supported, and 4.3.5 is not your problem. You don't say whether this problem occurs when on the cell data network (3G) or WiFi, so it's hard to know what is happening. See the User Guide, Appendix B.
Settings > General > Reset > Reset Network Settings
Restore in iTunes using a backup
Restore in iTunes as new, without using a backup.
Also, see this:
I am having network 3G connectivity issues with my iphone 4 since i upgraded to 4.3.5
The internet connection is erratic as sometimes it gets connected and sometimes not.
Wi-fi works fine but the problem seems to be on 3G network.
I tried re-setting the network settings and restored my iphone twice (once restoring with backup and once without)
nothing seems to be working.
pls help me with this issue
I'm having some of the same issues since upgrading to 4.3.5.
The WiFi on my 3gs just won't stay connected to any wireless network. What happens is it connects to WiFi, but the second I open mail/internet/any app requiring internet the WiFi connection drops and it reverts to 3g.
I've tried resetting the network settings. Same results.
I've tried resetting all settings. Same result.
I've tried restoring the phone via iTunes. Same result.
I never had any of these problems with 4.3.4 or 4.3.3. So there's absolutely no way to roll back?
I am having the same problems. I tried to upgrade my Iphone 4 to 4.3.5 on my laptop and the update hung for several hours. I finally disconnected and reconnected and got a message that I had to restore the iphone. This kept hanging too, tried for about 3 days. Finally went back to an old computer and restored the phone. For a while, I seemed to be able to sync partially if I started itunes whilst holding shift and ctrl at the same time. However, now when I sync with my current laptop, it keeps giving me a sync error ("cannot be synced an error occurred whilst writing to the device", occasionally it says "error 14" or error "50"). So at the minute i cannot sync at all. Have trawled the internet for a solution, with some ideas but nothing definitive.
Stupidly (yesterday in a brief period of optimism when I thought everything was sorted), I tried to upgrade my wife's ipad to 4.3.5 - same result. The ipad is now stuck and needs a restore, however i had never synced it with my old PC so am completely stuck.
I have tried removing itunes and reinstalling, that didn't help. At my wits end. Haven't told my wife about the ipad problem yet...that could prove tough - she loves that thing more than me and the kids!!!!
Can anyone out there help?