It's a strange to forget the password.
Anyway back to the question -

If you forget your password:
If you forget the password, you do not have write-access (or read-access in level 3) in the password-protected CPU.
To restore access, you have to reset the CPU and reload the program into the CPU.

Marcjan

Lots of questions lately about passwords problems.
Personaly i don't like it/ use it.

Give me some good reason to use or some good reasons not to use it.
Regards,
Marjan

Here's my take on the subject:

1.) Read/Write password protection:
No good reasons to use it other than trying desperately (and in vain) to protect your "intellectual property".

2.) Write only password protection:
I know a few sites where customers enabled it to "protect" the control system from any "quick and nasty" logic changes whichcanhelp to ensure theintegrity of the system (shift electricians had in one particularcase the tendency to quickly brigde things out in the logic or "fiddle" with it, rather than fixing the instrument problem or following the correct change procedure).

OEM's may usewrite protection to cover the warranty period of the machine (again, to avoid soemone "fiddling" with the control system which can lead to arguments who's fault is it that the new machine all of a sudden misbehaves).

Downside: Forcing is also not possible without password (which at least leaves a forcing table and yellow light behind so others are aware of it and it can be reviewed later).

Other rather useful case is of course Safety Integrated where write password protection of the safety program is mandatory.