EDIT This answer is 10 years old - it may not apply to newer proguard versions.
I think you need to add these flags at the very least (modify for you individual package names):
-keep class javax.** { *; }
-keep class org.** { *; }
-keep class twitter4j.** { *; }
Also, add these flags:
-dontshrink
-dontoptimize
-dontpreverify
Here's my whole config file: of my Proguard.cfg:
-dontshrink
-dontoptimize
-dontpreverify
-verbose
-dontwarn javax.management.**
-dontwarn java.lang.management.**
-dontwarn org.apache.log4j.**
-dontwarn org.apache.commons.logging.**
-dontwarn org.slf4j.**
-dontwarn org.json.**
-keep public class * extends android.app.Activity
-keep public class * extends android.app.Application
-keep public class * extends android.app.Service
-keep public class * extends android.content.BroadcastReceiver
-keep public class * extends android.content.ContentProvider
-keep public class * extends android.app.backup.BackupAgentHelper
-keep public class * extends android.preference.Preference
-keep public class com.android.vending.licensing.ILicensingService
-keep class javax.** { *; }
-keep class org.** { *; }
-keep class twitter4j.** { *; }
-keepclasseswithmembernames class * {
native <methods>;
}
-keepclasseswithmembernames class * {
public <init>(android.content.Context, android.util.AttributeSet);
}
-keepclasseswithmembernames class * {
public <init>(android.content.Context, android.util.AttributeSet, int);
}
-keepclassmembers enum * {
public static **[] values();
public static ** valueOf(java.lang.String);
}
-keep class * implements android.os.Parcelable {
public static final android.os.Parcelable$Creator *;
}
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