I had the same problem with my app manager. It worked with 3g but not with my home wifi (eircom). I searched for hours for a solution and only ever found one person on these forums with the same problem.

I recently moved into my own gaff and got Vodafone home broadband and it works fine with it. So basically i have no idea what the problem was.

Sorry i could not be of more help. Maybe try a friends wifi and see if it works with theirs.