sharedUserId in AndroidManifest.xml

[Emnaki Chih]

    
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.testapp"
      android:sharedUserId="myid"
      android:versionCode="1"
      android:versionName="1.0">
...
...

When I add the sharedUserId above (without which it works) and I run in Eclipse, even from a fresh VM, it gives the following message in console:

Installing testapp.apk...
Installation error: INSTALL_PARSE_FAILED_BAD_SHARED_USER_ID

So I am scratching my head, what is wrong?