This reallyb should be posted under "game bugs" since it does not have to do with your account. However this worked for me: 1) make sure you have a copy of Arena backed up on your computer. If not just hook up your device and it will do so. 2) On your iphone/itouch press Arena untill it wiggles. Press the X. This will delete the program from your device. 3) Connect device to computer. It will re-install Arena 4) Start arena on device
The only hitch with this is that you will loose any stats/tools levels you gained before the problem because it could not update it.