Unfortunately, not all programs work with casting.
Microsoft has been a longtime problem. They use tools to avoid pirating (recording) that often interfere with Casting.
If other programs are working but Media Player is not, then that is probably the issue. Make sure your system and Chrome browser are up to date, try another media program instead, or wait and hope Google figures out a workaround.
Hello and sorry for the delayed response.
I managed to get it working. It seems that the source and the recipient drop down are a bit tricky and a bit slow on my device so I was apparently clicking the recipient off when all I needed to do was click once more to turn it on - and away it went.
Thanks for your interest and suggestions.