Trouble opening certain attachments /links via the BlackBerry browser

I'm having trouble opening certain attachments/links through the BlackBerry browser.

works = opens in correct app.

5.0-9700
PDF-works
TXT-works
HTML-works
DOC-works
JPG-works
RTF-fails (goes to save)
DOCX-fails (500 server error)

6.0-9800
PDF-works
TXT-works
HTML-works
DOC-fails (goes to save)
JPG-works
RTF-fails (goes to save)
DOCX-fails (goes to save)

I'm opening these attachments through the browser via the following code:

BrowserSession bSession = Browser.getDefaultSession();
bSession.displayPage(urlForAttachment);

Both of these devices are connected to a BES.

Does anyone know how to resolve this issue so that all of the attachments/links open correctly through the browser?

Update 2 Feb 2011:

So in 5.0 it was an MIME settings issue. Here are the correct settings on the server:

docx = application/vnd.openxmlformats-off开发者_Python百科icedocument.wordprocessingml.document
doc  = application/msword

In 6.0 it seems to be a browser issue. When we upgraded to a new build of 6.0, here is the error we got:

The requested URL could not be retrieved

Sorry, we can't open the web page that you requested because access was denied. If you should have access to this web page, contact your wireless service provider.

Error Code: 10001

Any ideas?

Note: the server doesn't even log an attempt to communicate.

Thanks!

Check that the server is sending the correct content-type http header for the content.

It would also be more useful to show your works/fails table against the content-type values, instead of the file extensions.