I just finished that particular mission. Like everyone else I was having major issues on Venus finding the last "High Value Target". I jumped on my sparrow in Nav mode and went as far as the steps where as I found out there are no mission beacons, On the way back however I headed to the Citadel where the quest that captures Skolas finishes and in Nav mode again I spotted the icon on the beacon that signals a "High Value" target. That's the one with the star in the middle. The last target turned out to be a Vex Minotaur just before the lift that takes you up to the top of the Citadel. He was a pretty easy kill with my Arc Sword, being a level 40 Titan helps too. I also got the 25 legendary marks, as well as all the other goodies, so it sounds like the glitch that people were having dramas with is fixed too. If you are having dramas finding it jump on your sparrow and go looking like I did, it saves grinding and grinding and grinding like I did for about 3 hours waiting for it to appear near Ishtar Cliffs etc etc. I just wish I had of thought about going for a ride earlier. It is hard to resist the urge to jump off your sparrow and kill something though. Hope this helps anyone struggling. Happy Fallen killing! Cheers Greg