There can be different reasons for the message "This accessory is not designed to use with the iPhone":
It is possible, that there are open applications in the background of the iPhone, which have not been used for a while. In the "Standby Mode" these running Apps can use a lot of computing resources and battery life of the iPhone. The more programmes running in the background, the higher the computer usage and energy consumption. Depending on the iPhone generation and the number of programms running, the iPhone stops to respond correctly or slows down the processes. The iPhone 3 is more sensitive than the iPhone 4.
You should close the programs running in the background : In this process no data or Apps will be deleted. Please tap the Homebutton on your iPhone two times. A new window on the lower screen will open. This window shows which programms run in the background or standby mode. Tap an App for two seconds until a small minus sign appears. Tap on the minus sign of every App and close all of them one by one. When all the applications are closed, close the bottom window by pressing the Homebutton once. Now start the App again and try the Medisana device.
If these steps, as described before, do not help, please try the following: iPhone "Softreset". With "Softreset" no data or Apps will be deleted. Please press the Homebutton and the Stopbutton at the same time until the "grey apple" appears on the iPhone and it reboots.
The original operating system (iOS) is not installed on your iPhone.
Please connect your iPhone with iTunes and update the operating software.