Jan. 21, 2013 did the gorn minefield fleet action several times now. still can't collect the reward from Halting the Gorn Advance mission. must still be broken
I've had no problem getting the reward.
1) Are you taking the "Halting the Gorn Advance (Daily)" version of the mission? There is also a "Halting the Gorn Advance" mission which has its own rewards, separate from the Dilithium/Fleet Marks reward of the 'Daily' version. The 'Daily' version is not necessarily available every day.
2) The "Daily" version requires that the 4 Mineral Samples in the board be collected. Check your mission log for the mission and it will say 0/4, 1/4, etc.
3) If you are trying to complete the 'regular' (non-"Daily") version of the mission (why?), i think you actually need to go over to the system and enter it, not just queue it up in the PvE queue.