android java.lang.NoClassDefFoundError even though the class IS there

Question

Skip to my EDIT section below - new project setup and new question there. I left the original stuff here for context...

I'm getting a NoClassDefFoundError in my Android project - in this case it's complaining that it can't find the the UserVoice plugin I just added:

Triggered by this code:

package com.mycompany.myapp;
...
import com.uservoice.uservoicesdk.Config;
import com.uservoice.uservoicesdk.UserVoice;
...
public class MyActivity extends Activity {
    ...
    public void onCreate(Bundle savedInstanceState) {
        ...
        super.onCreate(savedInstanceState);
        ...
        _configureFeedbackWidget();
    }

    private void _configureFeedbackWidget() {
        // It gets past this code, which contains stuff in the same 
        // "uservoicesdk" package as the problem class. 
        Config config = new Config("myapp.uservoice.com");
        UserVoice.init(config, this);
    }

    public void showFeedbackWindow(View v) {
        // Triggered by a button on the page
        UserVoice.launchUserVoice(this);  // Error is triggered by this line
    }
    ...
}

However, I cracked open the .apk (using dex2jar) that was installed and manually verified that the PortalActivity class, that it's complaining about, IS there:

What could cause Android to not find the class?

EDIT:
I've changed around my project dependences & Java Build Path settings, and this is what I have now:

!

I cleaned/re-built - no errors, and now I'm seeing the following:

1. MyApp.apk no longer has the com.uservoice.uservoicesdk package in it. That package is now in PortalActivity.apk, which I can see, from the console, is installed separately from my .apk.
   
   Console output:

Uploading MyApp.apk onto device 'LG-MS770-275bcf0'
Installing MyApp.apk...
Success!
Project dependency found, installing: PortalActivity
Uploading PortalActivity.apk onto device 'LG-MS770-275bcf0'
Installing PortalActivity.apk...
Success!
Starting activity com.mycompany.myapp.MyActivity on device LG-MS770-275bcf0

2. Now my app dies during the _configureFeedbackWidget() method, above, with the error java.lang.NoClassDefFoundError: com.service.uservoicesdk.Config.

So, what is the correct way to reference the PortalActivity project from my project such that my project can find PortalActivity's classes at runtime, and not just at build time?