Usually, this is caused by a problem with your internet connection or the settings on your phone.
Please try these steps to fix your connection:
Reboot your phone (power off, power on).
Upgrade WhatsApp to the latest version: Press Download Now - once the download is complete, open the file to initiate installation.
Turn Wi-Fi off and back on (Android Settings > Wireless & networks > Wi-Fi).
Try connecting to different Wi-Fi hotspots.
Turn Airplane mode on and off.
Make sure that data is enabled (Android Settings > Wireless & networks > Mobile networks).
Go to Settings > Data Usage > Menu button > make sure Restrict background data is unchecked.
Contact your mobile provider and make sure your APN settings are configured correctly.
If you are often connected to Wi-Fi, check your Wi-Fi sleep policy (Homescreen > Menu Button > Settings > Wi-Fi > Menu Button > Advanced > Keep Wi-Fi on during sleep) and make sure it is set to "Always" or "Only when plugged in."
Reboot your Wi-Fi Router.
Verify that you receive your Google mail emails on time.
Delete and re-install WhatsApp (Note: This will erase your chat history. Be sure to run a manual backup beforehand: WhatsApp > Menu button > Settings > Chat Preferences > Backup conversations).
Upgrade your Android OS to the latest version for your device.
If you are able to connect on Wi-Fi but not on your mobile connection (EDGE/2G/3G), double check your APN configuration with your mobile provider. You must be able to send and receive non-web traffic in order to use WhatsApp.
