SpellerPages getting 403.1

When running the spell check We are getting:
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The page cannot be displayed
You have attempted to execute a CGI, ISAPI, or other executable program from a directory that does not allow programs to be executed.
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Please try the following:

Contact the Web site administrator if you believe this directory should allow execute access.
HTTP Error 403.1 - Forbidden: Execute access is denied.
Internet Information Services (IIS)
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We are running IIS 6 on Windows 2003 server. I installed IIS FastCGI and Aspeller on the server. We configured the directories as described in: http://docs.fckeditor.net/FCKeditor_2.x ... 003_Server
(although the "you" in the first bullet is ambiguous so I configured for IUSR, IWAM, and IIS_WPG).

Still am getting the error. Everything works fine on our local development boxes (although we are running XP there).

One other clue: we wrote a "hello world" php page and it works, so I don't think it is the php setup, but rather when the speller php page calls the Aspell executable.

We suspect the issue is related to permissions on something we have overlooked. Any and all help will be appreciated.

Mark