Command /testfor @p[ x~,y=,z=*, R=1] resultsThe entity UUID provided is in an invalid format

mistakeningly hit enter, if someone could please delete this.

/testfor @p[x=0,y=0,z=0,r=1]
it only outputs "The entity UUID provided is in an invalid format" if the player is not found.

What Arron Rhodes said about the message is completely wrong. It can also display that message whenever the selector syntax is wrong.

I was only partially wrong, although I sholdn't have used the word only.