What you can try too is right mouse click on your character portrait and select "reset all active phases" then try the gold launch button
you may not be at the point to select the solo version until after talking to lana
EA QV TeamAbandon [STORY] Flashpoint: Assault on Tython, that might be interfering with your A Traitor Among the Chiss mission.
Reset of phases can only occur in non instanced areas like fleet for example
Did removing the flashpoint mentioned by @EA_Kipling make any difference ?
Do a repair scan per this link just to be sure it isnt file related
