XML FMC data not showing

I installed an add-on aircraft to my FSX that uses SID/STAR data in the TXT format, however, an add-on already installed, which has its FMC procedures in the XML format, now doesn't show the XML data on the left hand page of the FMC. The TXT data is still there.I has been suggested that I uninstall both FSX and my add-ons but this is such a pain! Does anyone out there know the inner workings and secrets of the FMC data system, and if so, can they tell me;

1. Why this may have happened?
2. How can I rectify it?

Computer OSWIN7 64bitFSX SP2Terry Gale