软件包 natbib 警告和参考书目问题

Question

下面这些错误是什么？

Package natbib Warning: Citation `Krishna2014' on page 16 undefined on input li
ne 502.

[16 <./figure/aks smr.png>] [17] [18]
! Undefined control sequence.
l.560 \Bibliography
                   {figure/bib}