Check to see that you are using the latest version of Tango on your device.
Ensure that your device is connected to a strong and reliable network connection. Try connecting your device to a different network connection, like a free Wi-Fi connection to see if the problem persists.
Try force closing the Tango app and any other applications that may be running in the background. Relaunch Tango and see if that allows the video message to send or play.
If the above mentioned doesn't resolve the issue, please submit a support request and someone from our support team will assist you.