We may not have permission to unlink vp.dir

$ /etc/init.d/varnish_master restart
Stopping Varnish Cache:                                    [FAILED]
Starting Varnish Cache: Assert error in mgt_VccCompile(), mgt/mgt_vcc.c line 302:
  Condition((rmdir(vp.dir)) == 0) not true.
  errno = 13 (Permission denied)