Hi. This might happen if you downloaded the Whatsapp .apk file using the AG Chrome Selfie's browser - (the problem must lie with the 'Download Manager' app). Try downloading the .apk file from another phone and send it to the Selfie via Bluetooth. Then access your Bluetooth folder using the File Manager app and tap to install the APK file. Let us know (and please with a bit more details) if you run into another issue.