Install 64-bit omnidriver.
No joy.
Install 32-bit omnidriver.
No joy.
Uninstall all that shit.
Restart.
Run registry cleaner.
Restart.
Install the native 32-bit TWAIN driver.
Install the 3rd party omnidriver.
Restart.
Scan slides.
This is a PITA but still better than 30 years ago when NOTHING worked together.