A few weeks ago, at Google's request, gMaps Pro was pulled from the Windows Phone Marketplace due to a copyright infringement request.
According to the developer Alexey Strakh, gMaps Pro was originally to be hidden from the open Marketplace while the app was re-branded. For some reason (Alexey notes a problem with Microsoft) the app wasn't hidden and eventually pulled. Gmaps was flagged for violating Google's trademarks, something we reported on earlier as other apps had the same problem.
The skinny of it all is that gMaps Pro v1.23 is now available on the Marketplace but upgrades from previous versions are not possible without paying for the updated version. Because it was pulled or deleted from the Marketplace, v1.23 is considered a new app creation and updates to the old versions not possible.