It is a complaint about your stylesheet. There is a known bug in some
versions of Styler, sorry I don't know the exact versions, where we
could write out a stylesheet that was invalid according to the DTD for
Styler. As I remember it, it is pretty easy to open the stylesheet as an
instance and see the issue if you need to repair the stylesheet.
I believe this bug is fixed in the upcoming M040 drop but I don't
remember if it got fixed earlier than that as well.
Software Development Director
Arbortext - PTC