it said it would make a back up copy but I forgot to write it down.
It's named "exe.xml_Before_Addon_Manager.xml / dll.xml_Before_Addon_Manager.xml" in your %APPDATA%\Microsoft\FSX folder, the filename has been chosen to be fairly self-explanatory...
Just a note seems that I'm not the only one who is having this issue as posted in the pmdg forums
Sure you are not the only one having this problem, but that doesn't mean it's a problem that has anything to do with any of our installers. The XML file corruption has been confirmed to be caused by ASN, and it seems it has been FIXED by ASN in a recent upgrade.
Our installer is just INFORMING you of a problem, and gives you the CHOICE to either create a NEW file from scratch, or abort the installation, in case you might want to try fixing the problem yourself. Since you opted to create a new file, it obviously contained only the FSDT lines, "NEW" means of course a new file which is as if you just installed FSX with no other addons, just with the FSDT-lines added.