I just don't get the same experience. I find that any of the Real Player Alternatives will run fine all week. But without fail between 18.00 and 20.15 every Friday the alternatives if I have Radio 4 playing go down. I have repeated exactly the same symptoms on a laptop - on the same day.
The only way I can the get Radio 4 back is to download Real Player or Real Player updates. This has been going on since the middle of last year and in the end having tried just about every permutation of players without winning I've accepted I have to put up with Real Player!
Several e-mails to the BBC have produced a string of the expected gibberish - i.e. there is no "alternative".