This actually looks like your scanners have been using a trial version of Rebex FTP for a long time, and someone somewhere has been periodically renewing the 30-day trial period until recently.
Have you or the scanner software vendor purchased a Rebex FTP license? I'm unable to find you in our customer database, so please contact email@example.com to sort this out!
In the meantime, adding this code to the application will enable a 30-day trial period starting today:
Rebex.Licensing.Key = "==Al5Gzv8j5BLqeZ4HK1AsMq4gybA2QVFaoEDHahPJ0R/4==";
Update: The wording of the trial expiration error message looked unfamiliar at first, but I have since learned that we have been using that wording in versions released in 2011 and before. Interestingly, the error message was only present in the trial version, and was missing from the full (purchased) version. This indicates that your scanners have indeed been using a very old 30-day trial version of Rebex FTP.