On paper, all legal matters are handled in a feudal fashion. Issues are taken to your liege lord, who rules, and you live with it. The problem is that that is simply not practical when you have the kind of population and business that happens in Amber, so a system of courts has evolved over time to address these matters.
First and foremost, there is the simple matter that the king shouldn't be bothered for every little thing, so Oberon created magistrates. Few in number, the title gave them authority to walk among dukes and princes, and allowed them to pass judgement in places far from the throne or in matters too important for lesser courts but too small for the king. Perhaps more importantly, their job was to see that matters legal went smoothly, and to that end they served as advisors and investigators in any matter that might hold the kings interest. While they could not, for example, rule on a matter internal to a great house, or between two dukes, they could look into the matter so the king was as prepared as possible to do so. The magistrates were also able to appoint and remove judges.
Judges made up the lower court, and oversaw day to day matters of trade, taxes and petty disputes. Where being appointed a magistrate was a great honor, being appointed judge was a slightly shabby but perfectly passable job for a lesser son of nobility, or an excellent opportunity for any other citizen. The bulk of day to day legal matters are handled by judges.
Unfortunately, matters of succession have muddied the waters greatly. Eric's ascension involved suborning or removing many magistrates, and he did not have the time to replace them. Those few that remained have most gone to ground - not only does the legal question of succession put a target on their forehead, they are men of power who have made powerful enemies over the years, and the shield of their patronage has more or less vanished. They're smart enough to be somewhere else. And since only the crown (not the regent) can appoint new magistrates, there have been no new additions.
The immediate effect of this has not been obvious. Amidst the furor of transition, it has not been any great thing for the nobility to pass their own rulings, and the judges have continued to do their jobs. However, without Magistrates to oversee or (more importantly) replace them, the judges have begun pushing their bounds. Corruption is growing more commonplace, and may soon explode into a full blown epidemic.