I once set up a read-or-append-only access to a file (in addition to a password that provided complete access). The idea was that "ordinary" users, opening the file with no password, could browse existing records or add new ones, but not edit or delete existing ones ones

This is just something to check, but it seems that if the file were opening to a restricted layout instead of the layout you were originally using, it could cause this problem. Do you tell the file to go to a specific layout on startup?

The problem with "NO ACCESS" had something to do with groups. After (re-)reading the FileMaker Pro Help on groups, I still didn't understand what had gone wrong, but the Help did convince me that I didn't need groups. After I deleted all groups, the problem went away.

(If someone can point me to further explanation of groups, my education may be improved, but my immediate problem has been solved.)