Can't install app through iTunes

I bought Navigon Europe on my iPad the other evening as it's on special offer. I want it on my 3gs as well. Connect my phone to itunes. Select that I want navigon installed and I sync.
After the backup navigon just gets unselected, doesn't get installed. I have 3gb free space on the phone so I'm not sure what the problem is. I have tried a hard reboot of the phone.

I don't get any error messages, it just fail silently. Is the real issue logged somewhere?