title: Gradle release build with proguard: java.lang.IncompatibleClassChangeError and java.lang.NoSuchMethodError
body: <p>I recently migrated a project from Eclipse/Ant to Android Studio/Gradle. I am able to successfully build a signed release version of the project with proguard enabled. However, while testing the release version, I'm getting crashes from certain library projects and jars (which work fine when building a debug version).</p>
  
  <p>For example, when attempting to upload a file to Dropbox (a jar dependency), I get the following error:</p>
  
  <pre><code>java.lang.IncompatibleClassChangeError: interface not implemented
     at com.dropbox.client2.session.AbstractSession.sign(SourceFile:238)
     at com.dropbox.client2.DropboxAPI.putFileRequest(SourceFile:2199)
     at com.dropbox.client2.DropboxAPI.putFileOverwriteRequest(SourceFile:1571)
     at com.dropbox.client2.DropboxAPI.putFileOverwrite(SourceFile:1537)
  </code></pre>
  
  <p>Also, when attempting to sign into Box (a library project dependency), I get the following error:</p>
  
  <pre><code>java.lang.NoSuchMethodError: org.apache.http.conn.params.ConnManagerParams.setMaxTotalConnections
     at com.box.restclientv2.BoxBasicRestClient.()
     at com.box.boxjavalibv2.BoxRESTClient.()
     at com.box.boxjavalibv2.BoxClient.createRestClient()
     at com.box.boxjavalibv2.BoxClient.()
     at com.box.boxandroidlibv2.BoxAndroidClient.(SourceFile:49)
     at com.box.boxandroidlibv2.activities.OAuthActivity.startOAuth(SourceFile:71)
     at com.box.boxandroidlibv2.activities.OAuthActivity.onCreate(SourceFile:52)
  </code></pre>
  
  <p>I have other jars and library projects that work just fine...</p>
  
  <p>Again, there are no issues with either of these when building a gradle debug build (no proguard). I was also able to create a release build with proguard enabled using ant without any issues (able to sign into both Dropbox and Box).</p>
  
  <p>Any ideas?</p>