Might be worth trying the FAQ sample included with the DITA OT. It is a standard
specialization and known to work with the instructions provided in the XMetaL
Author Enterprise help.

The benefit of testing with that one is that if you get it working and you set
your specialization up the same way it should work too.

With a default install the DTD I'm talking about is located here:
C:\Program Files\Common Files\XMetaL Shared\DITA_OT\demo\faq\faq_shell.dtd