This is not a error, This is Warning,

Some hosting server showing this error due to server function. If you are facing this error you just need to follow these instraction.

1- Extract beetube.zip and find this file.

2- BeeTube--> extensions ---> class-tgm-plugin-activation.php

3- Open this file in text editor and remove from the first line.

ob_start();

4- And Remove this code from last line.

ob_flush();

After to remove this save file and zip "beetube" folder and install again . It will work fine.

Thanks