The iTunes library file cannot be saved. A folder was specified instead of a file.

I updated my iTunes to 12.3.3.17 version, While applying the latest upgrade to my iPad, i CONTINUALLY received the following message"

"The iTunes library file cannot be saved. A folder was specified instead of a file." I have NO idea what this is, why it is appearing or what to do with it.

My iTunes library is on an external hard drive and has been since the last time I lost EVERYTHING during a backup.

HELP PLEASE!!!!