Sometime this kind of problems will occur in drupal admin. At that time, we need to add the below line at the end of my.ini file to solve this problem.
max_allowed_packet = 32M
Step 1: paste the above line at the end of my.ini file
Step 2: restart your apache
Step 3: Check it and Enjoy
Step 4: if you are not an administrator user in your windows system, then you cant restart your apache, for that case you need to restart your windows system.