Got the title as an error message after downloading a replay and trying to watch it.
I did delete the file and tried again - same error.
I have successfully watched replays in the past. The game is from today (finished less than 20min ago) so there's no way it's on another patch.
MagicFlyingLlama2 votesI suggest you send the file to riot.
C:\Users\NAME\Documents\League of Legends\Replays and is a .ROFL file because riot is silly.
TSM BossQue1 votesdid you find a way to solve it?
ValyrianBlade1 votes[{quoted}](name=TSM BossQue,realm=EUW,application-id=LqLKtMpN,discussion-id=ujHcNLuA,comment-id=0001,timestamp=2019-01-26T17:42:54.920+0000)
did you find a way to solve it?
I don't believe I ever did.
The 2019th1 votesI had same problem yesterday. But it has fixed for me, I have tried couple times to delete the replay file in a users/documents/league/replays etc and then login again and download the game video back, after 2 or 3 times it worked :) Hope it will be fixed for you too !
ScriptedCode01011 votesDo exactly what this guy is doing and you will be fine being able to watch any replay it worked for me:) if not just reinstall best option left good luck 
https://www.youtube.com/watch?v=oEQpaPmbUp0