I use Spring Tool Suite (STS) when I'm working on Java projects that heavily use the Spring Framework. One gotcha that keeps getting me is the following message.

The Tomcat server configuration at \Servers\Pivotal tc Server Developer Edition v3.1-config is missing. Check the server for errors.

The message pops up when I try to drag a web project on to the icon for Pivotal tc Server Developer Edition v3.1 in the Servers tab. Eclipse can not read the configuration file because it lives in a project that is closed. In spite of saying open related projects Eclipse does not notice that the web server configuration project is related to my web application project and so I must open it explicitly. Opening the Servers project fixes it.