when you change/add bibliography in latex you might see that the update is some-times not reflected on the output. Reason: the bbl file is not updated. To force select BibTeX in MikTex and run Latex.
Remember that it’s not LaTeX that generates the BBL, it’s BibTeX.
1. Run LaTeX to generate the AUX file. It adds a line every time it finds a cite.
2. Then run BibTeX (executable: bibtex) to generate the BBL (from the AUX lines).
3. Then run LaTeX again, which will include the BBL.
4. Then run LaTeX again to make any updates corresponding to including the possibly massive BBL (e.g., updating your final page count on each of your pages, updating your ToC, etc.).
I don’t recall if TeXShop attempts to do this automatically. If it doesn’t, you need to make sure you run BibTeX whenever you need to update your BBL.
NOTE: This entry I found in internet. I donot claim it as my solution 
