That's weird because I got that error about iTunesHelper too, about a week ago.  I thought it was because I had upgraded to Lion.  However, it's possible that it was actually an iTunes update which did it; I think I remember seeing an iTunes update recently.

As far as what to do, delete the Login Item, because if it's not there it's not going to do anything.  But don't reinstall iTunes unless you find something isn't working.  Possibly Apple eliminated the iTunesHelper in the latest iTunes update but did not, as they should have, included some lines in their installer script to remove its Login Item.  You know, with 80 billion in the bank they've got more important things to worry about 

To avoid conflicts, BookMacster checks your Login Items when it launches to make sure that Bookwatchdog (the Bookdog background application) is not a Login Item.  If you have a broken login item, Mac OS X will not give all of the Login Items and therefore BookMacster cannot complete this process. 

Therefore, BookMacster tells you about the broken Login Item and tells you how to identify and remove it.  I wish that Apple would take care of this housekeeping for us when you log in, but they don't.