Convert Current PDF to PDF/X

Hi, Am using Acrobat 8.1.6.

Trying to follow Adobe instructoins for converting a PDF to a PDF/X:

http://www.adobe.com/designcenter/acrobat/articles/acr8ap_pdfx_03.html

When going to:

Advanced > Preflight

Selecting the PDF/X-1a (Coated27) profile, then

Options > Convert Current PDF to PDF/X (or so it should read)

Only thing is the line on the drop down menu reads:

Convert Current PDF to PDF/A

It then brings up another dialogue for PDF/A options, which is not what I want, I want to convert to a PDF/X.

Anyone had this issue, and any fixes.

Thanks

Rob