At the end of Ant Man, we are treated to two excellent post credits scenes that are setting up the future of the Marvel Cinematic Universe.

One of these scenes shows us that ;

Steve Rogers (Captain America) and Sam Wilson (The Falcon) have found Bucky Barnes (The Winter Soldier) who they have been searching for since the end of Captain America: The Winter Soldier. They begin to talk in hushed tones about what to do next, one of them mentioning that they "can't go to Stark. If only this had happened a week ago" (I didn't catch all the dialogue exactly, so this may be incorrect).

Obviously, this is set up for the upcoming Captain America: Civil War movie, but;

Why can't they go to Stark, and what happened a week ago? Where are they, and how did they find Bucky?

In general, the things seen in the Marvel Cinematic Universe (with the exception of Agent Carter and Captain America: The First Avenger) happen in real time, so I would expect this question (or at least parts of this question) to be answerable based on what we have seen so far.