The most recent release of PrintNode has an incorrect CFBundleVersion value ("4.0.0"), but the app appears to work normally after using defaults write to update that value and add a CFBundleShortVersionString value:
defaults write /Applications/PrintNode.app/Contents/Info.plist CFBundleVersion 4.17.14
defaults write /Applications/PrintNode.app/Contents/Info.plist CFBundleShortVersionString 4.17.14