Configuring OMA

[CJ]

On Exchange 2003 Enterprise SP2, our previous administrator has a setup with
an OWA FBA FE server, however he configured Outlook users to connect via RPC
over HTTPS to the BE server. I'm am now trying to configure OMA without any
luck.
Just using a browser if I go to https://backendservername/oma I get a login
prompt then this.

Server Error in '/OMA' Application.
--------------------------------------------------------------------------------

Runtime Error
Description: An application error occurred on the server. The current custom
error settings for this application prevent the details of the application
error from being viewed remotely (for security reasons). It could, however,
be viewed by browsers running on the local server machine.

Details: To enable the details of this specific error message to be viewable
on remote machines, please create a <customErrors> tag within a "web.config"
configuration file located in the root directory of the current web
application. This <customErrors> tag should then have its "mode" attribute
set to "Off".

<!-- Web.Config Configuration File -->

<configuration>
<system.web>
<customErrors mode="Off"/>
</system.web>
</configuration>

Notes: The current error page you are seeing can be replaced by a custom
error page by modifying the "defaultRedirect" attribute of the application's
<customErrors> configuration tag to point to a custom error page URL.

<!-- Web.Config Configuration File -->

<configuration>
<system.web>
<customErrors mode="RemoteOnly" defaultRedirect="mycustompage.htm"/>
</system.web>
</configuration>

I've tried method 2 from KB817379 but then I get 403.6 error. IP address
rejected. I assume since the BE server has a its own public cert, I cannot
use the FE server mentioned in method 1 correct? Anyone else have a FE / BE
setup where both servers use SSL and are able to get OMA to work?