Forum:Online game issue

This morning I played 3rd DLC (General Knoxx) on my PC. Now Im doing the mission that I have to kill Knoxx. The problem happened after I joined some online session, which triggered the new objective of "Super Marcus Sweep" into my quest log, and also appeared when I was playing solo (after I quitted the online game. Now the two mission are clashing together and I dont know what should I do next. Should I ignore Marcus' mission or try to delete it. Can you guys help me fixing with this problems?