UEFA decided a few years ago that all managers in the top league needed to successfully complete the Pro Licence course by 2010 or else face some sort of punishment, which could even have resulted in them losing their jobs. On previous occasions, some managers in the English Premiership have been able to operate without the licence but this has been the exception, rather than the norm.
The course takes the best part 20 months to complete and, according to Wikipedia, the licence is also needed to manage in European competitions - hardly a problem for us at the moment!
Gus is one of three SPL managers to complete the course, the others being Falkirk boss John Hughes and Inverness Caley Thistle gaffer Craig Brewster.