Hi, the reason this is happening is, unfortunately, that content is in the process of being removed from the platform. Usually when this happens you would not still see the option to play the episodes and our technical team are trying to fix this. Sorry for the frutstrating experience!
It is now December 2019 and this error code 21 is happening of every episode and programme on the kids programming. I tried to get help through the online chat where I spoke with 10 people, 6 of which ended the chat and the others timed out. My twins are going are not happy and I've had to pay for this non existent service. This needs to be sorted and someone needs to have a chat with your online help service.