I need to update fcp on my macbook pro (yosemite) but every time I try the app store asks me to enter my ID and password but it won't let me click on the ID box to put in my email and just gives me a generic example email in the box. I've tried just entering the password but then it tells me my account has been disabled due to security. I have tried changing the password but it does nothing. My details are working elsewhere, iCloud etc. It's just for fcp that it won't let me enter my email. None of my other updates required a password so they worked fine.
"firstname.lastname@example.org" does not appear to be a "generic example email", but rather the Apple ID used to purchase the copy of Final Cut Pro that is installed on your Mac. The purchase is tied to this Apple ID (which explains why you cannot change it) and in order to update the installation, you will have to provide the correct password for this Apple ID.