This was strange.
There are two fixes. DevLoader is not provided with Tomcat, so you can put the DevLoader jar in your classpath.
You can navigate to ~tomcat_home/conf/Catalina/localhost/. In that directory, you will find a file with the name of your project and the .xml extension. It is a context.xml file. Open the file with a file editor.
You will find this line:
Remove the line and Tomcat will start again.