I don't know if I should be suggesting this or not, nor do I know if it will help, but
if it were me having problems with my dll.xml file/no addon menu, I would look into this little tool:
http://www.flight1.com/files/FSXML.zipDESCRIPTION: "
FSXML is a unique management and repair system for the DLL.XML file that is used in FSX. It is not to be confused with a pure XML editor because it is specifically designed to edit, and help you repair, manage, and format the <Launch.Addon> sections of the DLL.XML file that is part of FSX.
In many cases this file becomes corrupt, or contain misordered <Launch.Addon> sections. Sometimes setup tools place incomplete sections, make incorrect alterations to existing sections, or place invalid characters in the DLL.XML file. And as mentioned above, some DLL modules need to be loaded in a specific order. This program helps you maintain all the above."
Basically, this program reads what is in your dll.xml file, and allows you to rebuild it, re-order it, etc. It will, in essence, handle any "corruption" of the file caused by incorrect Linefeeds or whatever the heck else causes the file to not interface correctly. I became aware of this tool when having installation problems with the Level-D 767. I have used it on one occasion since to rebuild my dll.xml file when my Addon menu disappeared for no apparent reason. No guarantees that it will fix your problem, it is just something I would try, just to make sure.
DISCLAIMER: I'm a relatively experienced FSX user, so my recomendation for this tool simply reflects what
I would do as the next logical troubleshooting step. If it fixes the problem great, if not, I could always get back to where I started. On the other hand, if you are an inexperienced fsx guy, or don't know how to back things up before mucking around,
don't use this. You had better read the instructions very carefully. If A2A people have a deeper insight into the Addon Menu problems that people are having and
doesn't recommend people mess around with this tool, I assume that they will step in and say so.