If called on a top-level (parent) ICommentThreaded object, it returns a top-level (parent) ICommentThreaded object that represents the next comment. Using this method on the last comment on a sheet returns null (not the next comment on the next sheet).

If called on a reply ICommentThreaded object, it returns a reply ICommentThreaded object that represents the next reply of a thread. This method works only on one thread. Using this method on the last reply of a thread returns null (not the next top-level comment).