If you previously used "modded" Poweramp and kept the data on uninstall (checked "Keep xx mb of data" on uninstall), the legitimate APK or Play build can't be installed as Android prevents app with the different signature from installing over the "modded" app data.
One solution will be re-installing that "modded" Poweramp again and uninstalling it without "Keep data" checkbox checked. That should allow legitimate Powermap installation.
And it's recommended to run some anti-virus/anti-malware app after that, as "modded" Poweramp usually comes with some sort of malware, usually increasing APK size 2-3x.