hey I am currently doing the quest missing in action and are at the part were I am supposed to Deliver proof to Avulstein.

However whenever i enter their house I get the "You are not supposed to be here" I have tried during night and day but always gets the same reply.

So is there anything I can do to fix this? Any console command or something?

Seems like a bug. On PC, you could probably select him in the console, exist the house, and move him to your location (moveto player). Talk to him then and see if it works. You could also try jumping the quest stage (setstage MS09 40 or setstage MS09 50). This is riskier and may glitch the entire quest completely so save beforehand.