Problem entering enemy sector

[Mephisto]

I have encountered this problem from time to time, too. IIRC it is a bug and it is fixed in the gold Version. The only thing you can do is dissolve the fleet and attack with each ship on its own. But don't sue my, I could be wrong about this.

[Suicide Junkie]

Is that sector a known minefield?
The "don't move through minefields" option might be at fault (it applies to minesweepers as well as other ships)