I am very sorry to say that our first released iPhone version (ver. 0.4.1) has a bug, which prevents you from saving our maps offline to the iPhone. I did a lot of testing, but in the end this bug slipped in, shame on me.
Version 0.4.2, which fixes this bug, was released on February 21st 2013.
For those of you, who want to work with our app in the meantime, there is a temporary workaround:
Use our online-map feature: Just check
Use online maps in the settings menu and go ahead. Needless to say, that you have to be online for this to work :-(