I just did everything I could to complete the campaign mission to free Earth from the Drengin and the precursor shield. The Drengin are destroyed, the Crusader is parked right next to Earth - now what? Although the dialog announced the Drengin had been destroyed (and they no longer show in the diplomacy screen), the victory conditions/objectives still shows Destroy the Drengin as unchecked. It is also optional, but in any case the objective to lower the precursor shield is unfulfilled, even though the Crusader is right next to Earth -and it is not an option to move it onto the same space.
If anyone knows how to complete this mission, please advise