Behind Enemy Lines driving me nuts

[CGA1]

I'm trying to complete "cross enemy defensive line" but it seems impossible. I get all my three men as far as i can on the road after detecting the minefields but nothing happens. Trying to move them to the flashing circle doesn't work, they can only be moved alongside the mountain (but past the enemy line). What am I doing wrong? Do the missions have to be completed in a certain order for it to work? I have blown up the tanks already.