I found this at a website:
"Currency has strict printing standards, is easily accessible, and highly reproducible. Alas, scanners and printers have also created a problem with amateur counterfeiters. Canon, HP, Adobe are among others who have voluntarily embedded software to refuse to scan modern currency from various countries, but they do not readily publicize this restriction.
The currency detection system in the LiDE generates a TWAIN driver error rather than a message that states scanning of currency is prohibited. However, it will scan older currency and any other print material without issue. Unfortunately, for us 'old dogs' of technology that reach for currency as a test subject, the TWAIN error drove to me troubleshoot drivers, hardware, and software to check for errors. I later confirmed the currency detector with Canon. It is not documented in [Canon's] website."
Anyone buying one of today's newer scanners will no doubt encounter this problem...