Cannot retrieve properties at this time - Content Editor Web Part Error

Sometimes, when I edit content in a Content Editor Web Part, I encounter the following error :

Cannot retrieve properties at this time

The solution is simple, do the following.
On the SharePoint Server:

1. Open IIS Manager.
2. In the left pane, expand the server where SharePoint is installed and then click on Application Pools.
3. Right-click on the application pool from which you get the error.
4. Click on Recycle.
5. Close IIS Manager.
6. Retry saving your work.