EnglishMan

Apple ID. They changed the passcode (I will use password from here on) associated with the AppleID probably via appleid.apple.com.
However, that new password would have to be entered into the iPhone (Settings-iCloud) to have that iPhone activate iCloud backup, else it can't connect.
Somebody probably thought they would change the password to get at the data in iCloud, found out the data hadn't been backed up in months (or at all), then learned that they couldn't get the iPhone to start auto backup without entering the new AppleID password in settings, and because they didn't know the original password, could not set it back. 
Now they are stuck with an iPhone that can't back up to iCloud and they can't change to the new password because they don't know the 4-digit PASSCODE to access the iPhone. Thus, because the FBI screwed up, they want Apple to create a software hack to bypass the 'Wipe data after 10 wrong passcode attempts' so they can brute force the device; easier to do with only 4 numeric digits, especially when you have to use 4, not 1, 2 or 3.
Once the iPhone passcode is broken, then the FBI can enter the NEW AppleID password to get the phone to sync with iCloud, but then it won't be necessary because they can now simply copy everything to a computer.

In other words, they want Apple to save their butt for doing something they thought was smart, but didn't work, so they try Plan B and Apple balks.

CORRECTION: Password changed by SB County, not FBI. Still, FBI should first go after county for screwing them, not Apple.