Question mark in citation using Bibtex

Question

Today I opened my Latex document and suddenly all citations turned to [?]. What surprised me is that everything was just perfect but suddenly today I found this issue. Has anyone faced such an issue before? If so, would you mind providing me how you solved it?

I use Texpad in Mas OSX.

Thank you

Solution

This is because your references have changed. Take a look at this link. It explains your problem very well and gives solutions. Good luck! https://tex.stackexchange.com/questions/61307/question-mark-instead-of-number-for-reference