I've had that before, also had to kill the same target 3 times, they kept respawning and interdicting me. It was all good as they had a 1m+ bounty which I collected 3 times.
The best of these is Odyssey foot missions, I take an assassination mission and it fails the second my ship touches down 1km from the base. There was 8hrs still on the timer...didn't even get to disembark
You've got to love the sheer number of bugs present in the ED mission system...it's quite staggering.