I am semi-retired ATM, but I'll try to help you out!
Make sure you are using B7 (from Oosat2 NOT B2 from Oosat1)!
Check Assassins.oxp is in AddOns. Sounds obvious, but killer instinct couldn't get it to run. Turned out he had 2 copies of Oolite on his system and had put it in the AddOns folder of the copy he wasn't running!
First thing test Assassins is being read!: Can you load up Oolite and say N to load new commander? Then use the right arrow to move through the ships on the screen (your gonna have to move past the Native Ships), keep cycling through. Are you seeing ships like "Vintage Adder" "Armoured Passenger Liner" "Nemesis" "BattleBot" etc. This'll test that Oolite "knows" Assassins.oxp is there. I'm pretty sure the OXP code is OK as so many people have played it to completion and I haven't altered it for a few months. (See the Assassins Guild Beta thread under Expansion Packs).
Something should happen to you the first time you dock with more than 200 kills. Make sure though you do not have Military.oxp or Thargoid Wars installed as there is a chance of an OXP clash.
EDIT: Should mention of course the you should put these OXPs back in once you've finished Assassins. Its just that if you try to play three mission OXPs at the same time (not only will you find things a bit hairy!) but there is a small chance each OXP will try to give you a mission briefing at the same time. This means you may miss a mission briefing (eg See an Assassins briefing but miss a Military briefing or visa versa). You can still do both missions (and your description on the F5 screen changes) but you'll have missed some of the plot and won't know exactly what your meant to be doing! Best to play one mission pack at a time.
