For the trackbacks to be functional in a particular blog, you need to enable the following options on the blog's Form tab:
•Enable trackbacks - this option enables displaying of the trackback URL with each blog post and inserting of trackbacks as blog comments
•Allow anonymous comments - trackback comments are in fact anonymous comments, so this option needs to be enabled for the comments to be inserted
•Open comments for - this option defines how long after the insertion of the blog post will inserting of blog comments be possible; trackbacks can also be inserted only within this period
The Allow comments option must also be enabled on the pinned blog post's Form tab so that the comment can be inserted.