Same problem here trying to download a free app (Whatsapp) to my Nokia 920. However what I can't understand is that I can download other free apps just fine.
WiFi is good, Location is good, Mains power is connected. Been trying literally for 8 hours.
Same problem. MS has made announcement on their support website : http://answers.microsoft.com/en-us/winphone/forum/
January 15, 2013
Windows Phone Store is currently experiencing some problems with purchasing and billing. You may receive one of the follow error codes while purchasing an app from Store on Windows Phone: c101a006, c101a007, 805a01f4. Or, you may see a "service not available" error message. This outage impacts both Windows Phone and WindowsPhone.com purchase experiences. Free app downloads are not affected.
My 920 works fine no probs with downloading apps have had it for a week my wifes which I set up gets the Error 805a01f4 on trying to download certain apps like Facebook Pro When her phone gets this error I have used my phone side by side with hers downloading same program straightt away with no problems is it something that has been set up on her phone or a bug hard to say love to find an answer though