when I run iRidium application on the panel, it controls (sends request to) all the KNX devices in the KNX line. I mean I have only one button and one single command object assigned to the  Press event of the button, but it seems that the application sends many commands to KNX IP router and tries to control (interview) all devices (on/off all lights etc.) at startup.
I simply imported the ETS file in GUI Editor and used one of the commands. I use KNX IP router for application. Remember that it happens only at the startup of the application. What can cause this?

It is normal. iRidium requests all feedbacks written in the Feedbacks tab of the driver at project start. It is how the start initialization of the project happens.
In the Feedback tab of driver you need to leave only those feedbacks from which you need to receive feedback. Feedbacks available for reading should have the Read field marked in the ЕТS settings.
The only solution to let clients control there home externally in a secure way is using a VPN.
The are plenty of routers on the market that act as VPN gateway to the local network.  Be wary of the cheaper products because the VPN throughput is usually quite low.  Also some  manufacturers will supply their VPN routers with some sort of licensing scheme based on the number VPN connections allowed.  You should also consider the fact devices that use multicast \ broadcast packets may not work unless otherwise specified by the router.  Even if they do say that there is no guarantee without testing.   Typical example for this would be UPNP based devices, so Sonos, Apple TV, iTunes (Bonjour based).
If you see this messages in iRidium log:

[00:00:03.011]   CBAOS2xTCPDevice(1): Error: No item found 100
[00:00:04.540]   CBAOS2xTCPDevice(1): Error: No item found 100
[00:00:06.068]   CBAOS2xTCPDevice(1): Error: No item found 100
This message is not an error, this system message informs you about addresses which was added in your project but wasn't initialized on the BAOS side by some reasons. You can just ignore it.
It is simple to read Date and Time from KNX bus, but you have to use a special script to write a new value to the bus. Please take a look at the attached project.

"I created a Iridium projekt with KNXip and Modbus TCP connections to a Wago-Controller 750-849 (KNXip) and a 750-880 Controller (Modbus TCP). Everthing works fine.

The project contains about 250 KNX feedbacks. Evertime the application on iPad4/iPhone4 is started, iridium starts the initialization of the feedbacks. This takes about 20 sec. (checked with group adress monitor in ETS).
In this period commands are difficult to send/are not sended.

Is there a possibility to get an information (e.g. token) when the iridium application starts, to trigger a popup ?
It would be helpful to show the information "initialization running, please wait" to the user and simultaniously block the other pages/popups, until initialization has finished.

The easiest way to setup an initialize page is  add a popup to your project that covers the entire screen.  Now add whatever text graphic that will inform the user that they have to wait.  

In the object properties of the popup there is a property called Lifetime,  its measured is milliseconds.  Put your wait time in there.

Now in the properties of the project file, add this new popup to the list of popups that start.
That's it you should have a wait page showing at the start of the project.
thanks for your proposal but the popup with lifetime limitation appears only if the iridium project is loaded by iridium transfer or if the app on the apple device is really stopped and completely new started. If i just push the Exit-Button on the apple device and afterwards tab the iridium app for starting iridium mobile, the application shows the last page before exit without showing the "information" popup. However the initialization starts every time. Any idea ?
It can be done using a iRidium script.   by attaching a listener to the IR.EVENT_ONLINE event the function in the listener would simply show the wait popup.

You can use this Project.

"No connection with the bus" means that the BAOS lost the connection with KNX bus. BAOS sends this error it the KNX bus is not connected physically.