The non-ABS 796 has a speedo sensor that operates from the rear disc. The disc itself has four dimples that are read by the sensor:
49240761A
The ABS 796, on the other hand, uses a similar disc but without dimples:
49210051A
It sounds like, either you've got an ABS disc by mistake, or you disturbed the speed sensor when fitting the disc.
Did you fit a Ducati/Brembo disc or an aftermarket one such as EBC or Galfer?