Groovy Conflicts with Grails

If you get this error:

Error creating bean with name 'pluginManager' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is java.lang.NoSuchMethodError: org.codehaus.groovy.control.SourceUnit.getSource()Lorg/codehaus/groovy/control/io/ReaderSource;

Check your WEB-INF/lib folder for older version of Groovy. In my case, this happened after installing some plugins using the STS plugin manager.