I have one copy of FSX deluxe for my desktop and one for my laptop so i can host a server and log in to it from my pc. The first attempt i tried was to use the one copy of fsx and activate it on both computers, this activated with out error. Once i connected to my laptop over the LAN an error msg popped up on my desktop stating that Duplicate licence id's were detected. I then bought another copy of FSX and uninstalled FSX on the laptop then re-installed the brand new copy and activated it online with out any problems, however the error or duplication still appears... Did i not remove it completely? not sure where these licence keys are stored but its not a duplication anymore. Very fustrating.
Call, they should be able to help.
When you deleted FSX and loaded the new one there may have been some lines left in the registry that needed cleaning out.