SW2 problem:prooceed to the never sector
 

In the center of map I have met many angorians, in mission details tell me to assists USS until main forces arrive but after main forces arrive game's cutscene appear and it back to main menu. What wrong with this? please help me.

RE
 

you have probably ended the game
if on the cutscene apears a butcher with a very big gun mounted and it shots in a middle of a fight and all ships dissapear
(i havent played that game a long time so it can be a bit difrent)