I found two existing discussions on this topic. However, they seem to be in inappropriate places and abandoned, so I decided to start a new discussion.
After starting City Lens on my Lumia 800 the main screen appears. Tapping any of the icons on the main screen, such as "nearby" of "food", will lead to the message "There was a problem. Please try again.".
This only happens when using the mobile network data connection. When using WiFi, the application works without errors.
Nokia City Lens Version 184.108.40.20621
Lumia 800 OS 7.10.8773.98
Firmware revision number: 1750.0805.8773.12220
Hardware revision number: 112.1402.2.3
Network provider: Bob/A1
Unfortunately the problem is the same after receiving an update to City Lens 220.127.116.1160.
Deinstallation and reinstallation does not help either.
Would really be great to hear if that's an issue that is known and taken care of.