Method Not Allowed

Everything seemed to install correctly and I think I followed the Readme files to the T, but I can't seem to figure out why I'm getting the error that I am. When I go to PM a user, I type the message and click send. Then the following error pops up:

Method Not Allowed
The requested method POST is not allowed for the URL /index.html.

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Apache/1.3.39 Server at XXXXXXXXXX.org Port 80

Has anyone seen this issue before?

I'm using:
Joomla 1.5 (in legacy mode)
FireBoard 1.0.4 Stable [ Teakwood ]
CB 1.1

Thanks in advance!
-E

No, it seems to be a server configuration error.