title: Gradle Sync Failed - Android Studio 2.3.1
body: <p>My code was working fine before the update. But after i updated to 2.3.1, it started to give the following error,</p>
  
  <pre><code>    Error:org.gradle.api.internal.tasks.DefaultTaskInputs$TaskInputUnionFileCollection cannot be cast to org.gradle.api.internal.file.collections.DefaultConfigurableFileCollection
  Possible causes for this unexpected error include:&lt;ul&gt;&lt;li&gt;Gradle's dependency cache may be corrupt (this sometimes occurs after a network connection timeout.)
  &lt;a href="syncProject"&gt;Re-download dependencies and sync project (requires network)&lt;/a&gt;&lt;/li&gt;&lt;li&gt;The state of a Gradle build process (daemon) may be corrupt. Stopping all Gradle daemons may solve this problem.
  &lt;a href="stopGradleDaemons"&gt;Stop Gradle build processes (requires restart)&lt;/a&gt;&lt;/li&gt;&lt;li&gt;Your project may be using a third-party plugin which is not compatible with the other plugins in the project or the version of Gradle requested by the project.&lt;/li&gt;&lt;/ul&gt;In the case of corrupt Gradle processes, you can also try closing the IDE and then killing all Java processes.
  </code></pre>
  
  <p>Please help. </p>