title: Grails 4 upgrade - Error message unable to find a single main class
body: <p>I am currently upgrading from Grails 3.3.10 to Grails 4.0.0. When attempting to run my project I get the following error:</p>
  
  <pre><code> Execution failed for task ':bootRun'.
   15:31:02.101 [ERROR] [org.gradle.internal.buildevents.BuildExceptionReporter] &gt; Unable to find a single main class from the following candidates [com.torque.Application, com.base.torque.ExtendedReportsController, com.base.torque.utils.NaturalOrderComparator]
  </code></pre>
  
  <p>Whether I try to run the project in my IDE or my terminal, I get the same error.</p>
  
  <p>I uninstalled and reinstalled grails 4.0.0 and I still get the error. Tried <code>./gradlew clean</code>, rebuilding, <code>killall -9 java</code> and still get the error.</p>
  
  <p>This was not an issue with previous Grails versions. No clue what is causing the issue with Grails 4 and no clue how to solve. Any insight towards a solution would be appreciated.</p>