How can you fix the bug in The Elder Scrolls 4 oblivion where it wont let you soultrap the last 3 souls in hermaes moras daedric quest?

Answer 1

It's a common bug, usually caused by casting the spell on two different creatures within 120 seconds, or twice on the same creature. The bug is can be corrected by applying the 'Unofficial Oblivion Patch' which sorts a lot of annoyances.

You can also use the console command 'player.setstage 000146AF 40'. That advances the Hermaeus Mora quest past the point where you need to collect the souls, you can go straight back to Mora's shrine to continue.