If the black voters as a group, had ballots rejected at a higher rate than that of the general population, there is a much more obvious reason. To vote in America is a right of each citizen, black or any other color. No matter what the color of the skin, each and every right also carries a responsibility . If a voter is unprepared to vote, then they should NOT have their vote counted. If a voter cannot follow extremely simple instructions on how to fill out a ballot then they should not have their vote counted.
Ignorance is curable with a little personal application.
Governor Jeb Bush and the State of Florida Legislature have provided millions of dollars to improve the system. This will make the mechanics of voting easier, and results will be known faster, but it will not solve the root problem. If an individual is too lazy to personally inform himself of the extremely simple rules of voting, then they should not have their voted counted. The color of your skin makes absolutely no difference. The men who died on the Normandy Beaches on D-Day did not offer their lives so future generations could be lazy.