Added ProGuard and now I can't build a release version
<p>I built a release version of my app and then decided I wanted to use ProGuard.  I added the following to my project.properties file:</p>

<pre><code>proguard.config=${sdk.dir}/tools/proguard/proguard-android.txt
</code></pre>

<p>When I try to build a release version, I get the following errors:</p>

<pre><code>[2012-11-28 17:47:37 - MyApp] Proguard returned with error code 1. See console
[2012-11-28 17:47:37 - MyApp] Warning: oauth.signpost.signature.OAuthMessageSigner: can't find referenced class org.apache.commons.codec.binary.Base64
[2012-11-28 17:47:37 - MyApp] Warning: oauth.signpost.signature.OAuthMessageSigner: can't find referenced class org.apache.commons.codec.binary.Base64
[2012-11-28 17:47:37 - MyApp] Warning: oauth.signpost.signature.OAuthMessageSigner: can't find referenced class org.apache.commons.codec.binary.Base64
[2012-11-28 17:47:37 - MyApp] Warning: oauth.signpost.signature.OAuthMessageSigner: can't find referenced class org.apache.commons.codec.binary.Base64
[2012-11-28 17:47:37 - MyApp] Warning: oauth.signpost.signature.OAuthMessageSigner: can't find referenced class org.apache.commons.codec.binary.Base64
[2012-11-28 17:47:37 - MyApp] Warning: there were 5 unresolved references to classes or interfaces.
[2012-11-28 17:47:37 - MyApp]          You may need to specify additional library jars (using '-libraryjars').
[2012-11-28 17:47:37 - MyApp] java.io.IOException: Please correct the above warnings first.
[2012-11-28 17:47:37 - MyApp]   at proguard.Initializer.execute(Initializer.java:321)
[2012-11-28 17:47:37 - MyApp]   at proguard.ProGuard.initialize(ProGuard.java:211)
[2012-11-28 17:47:37 - MyApp]   at proguard.ProGuard.execute(ProGuard.java:86)
[2012-11-28 17:47:37 - MyApp]   at proguard.ProGuard.main(ProGuard.java:492)
</code></pre>

<p>This is clearly referencing the signpost libraries I am using.  I believe I have added the required jars and libraries correctly, but I guess not?</p>

<p><img src="http://i.stack.imgur.com/KZKEX.png" alt="enter image description here"></p>

<p>I added the signpost jars via the "Add External JARs..." button, and added the commons-codec library via the "Add External Class Folder..." button.</p>

<p>What am I doing wrong here?</p>

<p>UPDATE:</p>

<p>I added a file called proguard-project.txt to the project's root.</p>

<pre><code>proguard.config=${sdk.dir}/tools/proguard/proguard-android.txt:proguard-project.txt
</code></pre>

<p>Inside the proguard-project.txt file, I added the following:</p>

<pre><code>-keep class org.apache.** { *; }
-keep class oauth.signpost.** { *; }
</code></pre>

<p>I am still receiving the same errors.</p>
