What this said was that local law enforcement couldn't make arrests based upon federal law when the state law did not want people arrested for the same reason.
It's about the actions of local law enforcement in states with mmj laws.
http://reason.com/blog/2011/12/07/scotus-declines-to-review-appeals-court
U.S. Supreme Court declined to review a California appeals court ruling that said the state's medical marijuana laws are not pre-empted by the federal Controlled Substances Act
That leaves the legal situation as I described it in the October issue of Reason: While the Court has held, based on a ridiculously broad reading of the Commerce Clause, that Congress has the authority to stop patients from growing and possessing marijuana for their own medical use, even when such use is allowed by state law, it has never held that states are obligated to ban what Congress bans or punish what Congress punishes. Such a ruling would render states mere subsidiaries of the national government, forced to mimic its laws and policies, thereby obliterating what remains of the federalist system established by the Constitution. Fortunately, the Court does not seem ready to go that far.
There remains the question of whether federal law bars state or local goverrnments from formally authorizing, as opposed to merely decriminalizing, production and distribution of medical marijuana. Two months ago, California's 2nd District Court of Appeal said it does and therefore overturned Long Beach's licensing system for medical marijuana dispensaries. Although that decision still allows local governments to regulate dispensaries, it has created uncertainties that will have to be resolved by the California Supreme Court.