AnnouncerClassic.uax is a file that comes with the game, so I'm not sure why it's asking for it. You can always obtain that file unadulterated by reinstalling the game. Maybe try capitalising the file as it requests, instead of leaving it all lower case? Case sensitivity doesn't normally matter but it might fix it.
If the demo was recorded on a map/server that had a modified version of the AnnouncerClassic.uax, either embedded in LevMem or myLevel then it could lead to a version mismatch... but I don't really know. I couldn't run that demo you posted either, so maybe that specific demo is just corrupted for some other reason.