Cannot delete file, because it doesn't exist -- even if I say "rm *" -- and chmod works
Solution 1:
Take advantage of the commands with "positive" results to understand the case. There might be an extra special character (e.g., blank) in the file name. You could count characters to check this.
Post the output of
$ find . -maxdepth 1 -name cover.jpg
$ find . -maxdepth 1 -name "cover.jpg"
$ find . -maxdepth 1 -name cover.jpg | wc -c
$ find . -maxdepth 1 -name "cover.jpg" | wc -c
$ ls -1b | grep cover
$ ls -1b | grep cover | wc -c
$ ls -1b cover*
$ ls -al cover*