If you are trying to block a particular General Categories Ads in your Google's AdSense Account "Too big to Block" then it means that you have reached the allowed blocking limit in categories i.e. 50 and the category you are tying to block have more sub-categories then the amount you can block.
If you just hover your mouse over the ? (question mark) you see next to any : "Too big to Block" you will see the below text :
Code2care'smission is to share varied knowledge in technical and non-technical areas gathered during day-to-day learnings and development activities so that our visitors can leverage this portal to find solutions to their queries without re-inventing the wheel. Technical posts include Learnings, Tutorials, Video Tutorials, Code Snippets, Tips-n-tricks.