Took a chance and tried using ResEdit to change the locked bit and it worked. i had forgotten ResEdit can edit more than resource forks.

The file can't be renamed because it is locked. It also can't be unlocked.

The file originated on shared "Unix" drive. I moved it to Hard Disk but I need disk room and tried to delete it, which is when I discovered I can't delete or move it back to Unix without copying.

Disk First Aid found no problems. File remains undeletable.

I ended up with a rather large locked Toast file in Trash that I can't delete. Holding down the Option key causes the Trash can to momentarily to change to the empty icon but then returns to the full icon. I can't unlock it and attempts to move it to the Unix (shared) drive always results in a copy....