It is not possible to remove RealPlayer 16 from all the 400 computers at a time. It needs to be done individually on each computers. To do so, follow the below instructions:
1- Right click on RealPlayer
2- Select Properties
3- Click on Open File Location
4- Open Setup Folder
5- Double click on .r1pclean.exe
Now the RealPlayer will be uninstalled completely.
If you are still unable to remove RealPlayer, try installing RealPlayer 16 from the below link:
Once installed, follow the above instructions to remove RealPlayer.