It sounds like an intermittent connection somewhere in the wiring and or switches. Get yourself some good electronic contact cleaner and contact lubricant. Take every servo connection apart even into the receiver and spray with the cleaner. Plug and unplug several times repeating the cleaning then use the lubricant and spray the connections and plug back in. If you can spray inside the switch work it back and forth while spraying if not try replacing the switch. If this solves your problem then you have to consider the environment you are flying in is tougher on wiring connections and switches. If this is the problem cleaning may only temporarily remedy the problem. The only sure solution would be replacing everything that has a plug in connection. If you are using NiCad’s you might consider something called black wire syndrome
http://xternaldesign.com/blog/index....yndrome?blog=8
Battery packs can be a problem as the tabs are only spot welded in place and the tabs have been known to come off causing intermittent power. It would not hurt to try a different battery pack.
Dennis