can't sign into itunes store in itunes 11.4
after a power failure I was getting an error "We could not complete your iTunes store request. An unknown error occurred (-50)." when attempting to play an un-downloaded itunes match song.
So I tried logging out. Now I get that error, twice, when I try to sign into itunes. I'm running itunes 11.4 on macos 10.9.5 on a core i5 mac mini. And yes, I know I could update itunes and macos but the interface gets worse and worse on every itunes release and I am not interested in upgrading further. In any case, iTunes Match is reported to still work with itunes 11.4 (https://support.apple.com/en-us/HT204230)
I also tried clearing the itunes store cache and creating a new itunes library and logging in from there.
ideas? thanks!
-trav