Exchange CAS Server running on IIS 7.0 – Spell Check Error

Following is the environment with exchange OWA setup in FE/BE.
E2k3 - BE Cluster
E2k3 - FE Server
E2k7 - CAS server (Windows 2008 - IIS 7.0)

Problem:
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OWA spell check works fine when OWA is accessed on the BE server and via the E2k3-FE server.
The OWA spell check fails only via E2k7 (Windows 2008 - IIS 7.0) CAS server and the OWA users get following error message while running Spell Check
"The spelling in this item can't be checked. Try again later"

Troubleshooting:
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Verified configurations on FE and BE server for IIS - looks good.
From IIS logs on E2k7 IIS7.0 CAS Server, IIS logs shows “404.8” as status code.
Here is how the entry in IIS logs looks like:
W3SVC1 POST /exchweb/bin/spell/owaspell.dll - 443  404 8 0 1430 814 0
Created a sample page like time.asp and browsed that - http://servername/exchweb/bin/spell/time.asp
Sample page also fails with 404.8 status code.

Resolution:
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On IIS7.0 (CAS Server) look at ApplicationHost.config.
Take a back up of ApplicationHost.config and then edit/open the ApplicationHost.config with Administrator .

Locate and Change the following:

<hiddenSegments applyToWebDAV="true">
<add segment="web.config" />
<add segment="bin" /> <=========== Remove or comment this entry from ApplicationHost.config file and save the ApplicationHost.config file.

Now the spell check works fine on CAS server.

Related Blogs:
IIS7 blocks viewing access to files in bin and other asp.net folders
http://weblogs.asp.net/owscott/archive/2008/03/05/iis7-blocks-viewing-access-to-files-in-bin-and-other-asp-net-folders.aspx

IIS 7.0: security Element (IIS Settings Schema)
http://msdn.microsoft.com/en-us/library/ms690415.aspx