You can extract the key string from a backup. You can find the information in this thread:
unfortunately I don't have a backup. will a backup from another same robot help?
It will be the same software options as that robot.
You will need the RW 4.0 software for RobInstall media pool. You listed the previous software as RW 4.0 rev91 (3HAC6811-1.91). If available, look for rev 127 (3HAC6811-2.27) as it was the last & most stable revision for RW 4.0 software. ABB may still be able to provide the software package, but not generate keys for it.
It will be the same software options as that robot.
You will need the RW 4.0 software for RobInstall media pool. You listed the previous software as RW 4.0 rev91 (3HAC6811-1.91). If available, look for rev 127 (3HAC6811-2.27) as it was the last & most stable revision for RW 4.0 software. ABB may still be able to provide the software package, but not generate keys for it.
Do you have this software with key?
No backup 
I have no keys for 4400. If you have another robot just like it, it would be best to use that backup to generate the key string.
ABB should still be able to provide the software, just not the key. If they cannot, create a separate thread asking for RW 4.0 - several awesome folks have provided this in the past.
decrypted key.id will work in newer systems. I wonder if they work in older ones too. I have been able decrypt a few key.id from older backups. If you had enough key.id with different options you could possibly rebuild your own key.id with the proper options. You would need all the different key.id for reference. Without the proper plaintext for the option, it's impossible to know what to add. It's ridiculous ABB can't generate keys anymore. They didn't even change the encryption. I’m not suggesting sharing the decryption software but maybe creating a database for the old unsupported robots like sc4+. Just a thought unless someone think there is some legal issues involved.
I have a similar robot in my neighborhood, it's a 4400 but it's a little shorter then my.
Is your robot a 4400/L30 or 4400/L10?
Is your robot a 4400/L30 or 4400/L10?
My is 4400/L30
And the other robot?
Only if you want to turn that robot into a boat anchor.
And the other robot?
I think is L10
That would probably have the same effect. Needs to be the same kinematic model.
Can the previous owner be contacted for a backup?
Can the previous owner be contacted for a backup?
unfortunately no, the previous owner is a company that sold the robots due to bankruptcy, so I don't have any documentation, nor a key, nor a backup. and I bought it from a third party who bought it at auction.
You could connect the flash drive to a computer and see if there is a backup on it. If there is, you only need to COPY a 'BACKINFO' folder.
Note: there are lots of variations of flash drives and adapters used for the S4C+. Connecting it to a computer may or may not be easy.
Maybe possible to edit key from other robot to the proper model.
I've seen keys decrypted, and options added and use of plaintxt key working on irc 5.. Im not suggesting anything like adding options but maybe edit the irb model in key if the 2 have the same options
