ispell gives "Wrong type argument: stringp, nil"

["Jeff D. Hamann" <jeff.hamann@forestinformatics.com>]

I'm setting up a new installation of emacs+auctex+ispell+balh, blah,blah. 
FLyspell mode turns on and when I attempt  and when I attempt to either 
spell check the document or simply check a word I get the following error in 
the minibuffer:

Wrong type argument: stringp, nil

I've added the following lines to my .emacs file:

; set some reftex modes
(setq reftex-extra-bindings t)
(setq reftex-plug-info-AUCTeX t)
(setq bib-cite-use-reftex-view-crossref t)
(setq reftex-cite-format 'natbib)
(add-hook 'text-mode-hook 'turn-on-auto-fill)
(add-hook 'LaTeX-mode-hook 'turn-on-reftex)    ; with AUCTeX LaTeX mode
(add-hook 'latex-mode-hook 'turn-on-reftex)    ; with Emacs latex mode

;; to make auctex aware of style files and multi-file docs
(setq TeX-auto-save t)
(setq TeX-parse-self t)
(setq-default TeX-master nil)

(require 'tex-site)

;;; try the flyspell stuff..
(add-hook 'tex-mode-hook (function (lambda () (setq ispell-parser 'tex))))
(setq ispell-dictionary "C:/ispell/dic/american.hash")
(add-hook 'text-mode-hook (lambda () (flyspell-mode 1)))

So I'm not sure what's going wrong. I've got an old installation on another 
machine (not sure the versions on the old machine) and it works just fine. 
I'm running emacs 21.3.1 with the ispell-3.2.06 downloaded from

http://www.fsci.fuk.kindai.ac.jp/aftp/pub/ptex/utils/

Any help?

Jeff.