'flex' is null or not an object in ext-all.js

I got this error for quite some time and i had no clue what was wrong in my page . Page consisted of only 2 panel controls . That's all

After playing around with some of properties of panel , the issue was resolved.

Issue in my case :

First panel had property layout: 'anchor'

Second Panel had property layout: 'border '

Resolution :

Changed the second panel property layout: 'anchor'

This might not be your case . This error is very generic and can pop up due to multiple reasons .