It has not been the best of years for mapping apps starting with the release of iOS 6. Apple's new, native Apple Maps got off to a poor start which led to the dismissal of those involved. The problem with Apple Maps was so severe that CEO Tim Cook felt compelled to make a public apology and suggested that iOS 6 users try Nokia Maps as a substitution.
One of the issues repaired was one traced back to the Windows Phone Marketplace that prevented the app from loading. Instead, a "Problem with app" dialogue would open. You can install Nokia Maps from your Windows Phone 8 device by clicking on the sourcelink.
source: WindowsPhoneMarketplace via WPCentral