@a, @p, @e and @r are currently not working within command blocks running a /testfor command.

For example, the command "/testfor @p[r=3,score_MoneyNeeded_max=0]" would normally fire if there was a player within three blocks with a MoneyNeeded score of 0 or less. Instead, the result box shows that "The entity UUID provided is in an invalid format."

As can be seen from the screenshot, my MoneyNeeded score is 0 or less, so the command block should have fired, but it hasn't.