There are a few reasons why you might not see posts on this friends page:
Musicians' Corner might have no friends defined. If you are Musicians' Corner, you can edit your InsaneJournal friends so they show up here.
Musicians' Corner might have friends defined, but all of their friend's posts might be over two weeks old (according to the times on our servers), and thus wouldn't be displayed here.
Musicians' Corner might have friends defined that post only protected entries that you can't view, because they haven't defined you as a friend in return.