"wrong file type, please select again"

i have a nexus 5. all of a sudden all my ringtones and notification sounds turned to default, and when i try to set any file as a sound i get a message "wrong file type, please select again". i get the same message no matter what file type i choose, includint the files that were my sounds until this morning. i tries to delete cache memory and reboot but that did nothing please help thanx gady