reverting file buffer does not work

[Pawel]

Hallo

I experienced some problems with reverting remote buffers.

M-x revert-buffer produces following error:
Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  directory-file-name(nil)
  tramp-flush-file-property(nil nil)
  tramp-cache-before-revert-function()
  run-hooks(before-revert-hook)
  revert-buffer(t)
* call-interactively(revert-buffer)
  execute-extended-command(nil)
  call-interactively(execute-extended-command)


GNU Emacs 21.3.1 (i386-redhat-linux-gnu, X toolkit, Xaw3d scroll bars) of 
2005-02-04 on bugs.build.redhat.com

tramp-version's value is "2.1.6"

tramp config: 
(add-to-list 'load-path (concat pp-tramp-dir "/lisp"))
(require 'tramp)

;; passwrods in the cache do not expire. Very usefull:)
(setq password-cache-expiry nil)

;; default tramp transfer method
(setq tramp-default-method "scp")


Greetings