It could be that anotherday.xhtml is just the file where the orphaned link occurs. Like I said before, you might just have to find each anchor (<a href="../blahblah"...>) in the code of that file and verify that the target file indeed does exist.
Search for "<a" in the anotherday.xhtml file in Code View and make sure that the file each one points to does exist in the epub's file list.