We all use UT2 at FSDT normally and nobody reported this problem before.
Try the following:
- Instead of having UT2 being loaded automatically by FSX, disable it in the %APPDATA%\Microsoft\FSX\EXE.XML file, by setting <Disabled>True</Disabled> in the line that loads UT2Services.exe, then start FSX
- ensure the Addon Manager is visible
- start the UT2Services.exe file manually, by running it from the FSX\Flight One Software folder
Try both running it BEFORE starting FSX, and running it AFTER starting FSX, and see if it makes any difference.