Can you open the original file with full access privileges?
If you can, then with newly converted files from that far back, enter the password in both the account name and password boxes. (I think that's how I got mine to open). If that fails, try leaving the account name field empty.
If you don't have the password to open the original file with full access privileges, then your only hope is to locate someone who has a password cracking utility that can open your file and tell you the password. I've never used such a widget, but have heard that some exist.
(If the script that runs on opening is the only obstacle, you may be able to "trick" the original file into opening without running the "on open" script.)
No I can not open the original .fp5 file either
Sounds like a password cracker is your only hope.