How to recover from “Object reference not set to an instance of an object” error blocking access to Umbraco control panel

I shocked when I found that I couldn’t access Umbraco control panel of one of the most important websites that my client has. It threw “Object reference not set to an instance of an object” error once I successfully logged in to the control panel.

After making backup and small research I found a way to recover from that annoying thing. The workaround was recycling the Application Pool that the website use.