I have come to the conclusion that when I updated my 2008 Maddog it placed a File called FSX Module in the root FSX folder. I was having all the same issues of insufficient fuel error message as well as the Vnav error issues. You must go into your root folder and take that module, the 2010 module out of that FSX Modules folder, that came with the update and place it into your normal modules folder. You can save the old 2008 module located there if you like, in a newly created folder so it doesn't conflict with the other module and just keep it where ever you like. The installer from Leonardo did not over write the old DLL like it should have and this seems to have been the problem, for me anyway. Restart your FSX and it will ask to run the new DLL. If you continue to have problems then you might need to edit your FSX CFG and delete the line of the old 2008 module command out of you FSX CFG. Make a copy of your FSX CFG first just for your own well being.
Did you get this sorted out?
This forum can be kind of slow, but people do respond eventually!