unable to save or rename files "the name entered contains one or more invalid characters"

[Moltres_rider]

I can't get any app on my phone to save a file nor can I rename any existing files, the same error occurs EVERY TIME!!! the error message reads "the name entered contains one or more invalid characters" I could even rename it "1.jpg" or "a.jpg" and it gives the same "the name entered contains one or more invalid characters" error message