When I plug in my iPhone I get "an unknown error occurred (-42408) this is a recurring problem please help!

I delete the SC folder like it says to do and it fixed it the first couple times but just last night I plugged it in and it said "an unknown error occurred (-42408)" and then it says "iTunes cannot read the contents of the iPhone. Go to the Summary tab in iPhone preferences and click Restore to restore this IPhone to factory settings" I don't know what to do! Please help! Thanks in advance