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You have 2 traffic files with the same flightplans.
This is usually the result of installing one or more of the ai packages designed to replace the default airline liveries with realworld liveries. An example is Chester's FS2004 International Airline AI Traffic Package,
http://www.simviation.com/fs2004jets43.htm. There are others out there, including 'Continental'.
Such packages often change the commercial aircraft used but use the default flightplans, including the default ga traffic.
If you install 1 of these packages without disabling the default fraffic file or 2 of these packages you end up with duplicate flightplans.
Traffic file are located in the...\
\Scenery\World\scenery\..folder. You can disable a traffic file by moving it to a different folder for safe keeping, or by changing the file name extension. I usually disable it by changing the .bgl extension to .bbb.
The default traffic file is 'traffic030528.bgl'. (Note: Chesters International package is saved with this name.)
Dave
At that time [1909] the chief engineer was almost always the chief test pilot as well. That had the fortunate result of eliminating poor engineering early in aviation.