To be sure my voting is understood, here are my results -
Starting in each case with a completely closed down app -
(1) Via WiFi (Same LAN as comfort) - connects okay
(2) Via WiFi (Access via internet) - connects okay
(3) Via 3G - data error.
When the app is started by (1) or (2) above, and then left running in the background, connecting via 3G seems to work okay when I leave the WiFi coverage/ switch off WiFi.
I want to emphasise what I said above. The main difference between our iOS 4 and iOS 5 phones is that the app does not, with iOS 5, remember the last system when it is started up from the "completely closed" state.
When the iOS4 phones completely close down the app, and then restart the app, the last connection is remembered and immediately the phone restores the "connected" status. No selection of the system involved is required.
When the iOS5 phones completely close down the app, and then restart the app, the connection is not remembered. When the system is immediately reselected in 3G, the "data error" happens.
On a couple of occassions starting up a completely closed app, with 3G coverage (no WiFi), and NOT selecting the system but leaving it on the "home" page, I have gotten a connection error warning dialogue. How could I get a connection error if I havent selected a system with which to connect? Other times the app dissapears into the background after a short time.