I don't think it's system related or necessarily Mularkey - though he's had some rough spots.
First, Daunte just isn't reading the receivers and hitting the open man. Part of the problem is that he's not playing his normal game - which includes scrambling - b/c of his knee. He's very slowed. He hasn't fully adjusted to the being a pure pocket passer as he never was.
Second, the Oline problems are making Culpepper even less comfortable and confident.
The biggest problem right now, is keeping confident, working hard and letting it come together. I really believe that all the skill position players would be fine at some point and that C-Pep can get to a point where he is playing very well - but, it will be slowed and may not happen b/c the O-line is SO bad and may never come around.