Try using an account name of "admin" and leave the password box empty. If that opens your file, go to File Options and reset your file top automatically open the file with Admin and no password.
Another circumstance that can produce this system is unique to the Mac OS. The "keychain" utility can be set to automatically open a file with a specified account name and password. If this utility's settings are changed or you open the file on a different computer that does not have this tool set up to enter the account and password for you, you suddenly get a log in dialog when you did not previously get one appearing when you try to open the file.
I entered "Admin" and everything opened!
I really appreciate your assistance!