Howdy-
That is odd. I am not sure; I just copy+pasted that command on my computer, and it worked for me.
A couple things:
1) what is your AFNI version? Output of: "afni -ver".
2) in that directory, what does the following show (don't know if it's possible that the files have bad permissions, for example?):
\ls -l *HEAD *BRIK* *nii*
?
--pt