I'm a bit surprised darwin doesn't like that. Anyway, here's a modification that doesn't use anything after '/usr/bin/perl' on the same line:

#!/usr/bin/perl  
!m;;;print "Just another Perl hacker"     
;s;
"rekcah lreP rehtona tsuJ" tnirp;;;m!    
lrep/nib/rsu/!#
[download]

An alternative:

#!/usr/bin/perl
print "Just another Perl hacker"
;!q!;
"rekcah lreP rehtona tsuJ" tnirp
lrep/nib/rsu/!#
[download]