[Android Q&A, Help & Troubleshooting] codethief:
I just tried BlankStore for the first time and, initially, was greeted with the following error upon creating the Android ID:

$ java -jar android-checkin-1.0.jar <email> <password>
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/http/HttpEntity
at com.android.checkin.Main.main(Main.java:17)
Caused by: java.lang.ClassNotFoundException: org.apache.http.HttpEntity
at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:323)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:268)
... 1 more

Obviously, and as was already pointed out, I was missing some dependencies. For me, however, there was a trick involved:

Since the android-checkin-1.0.jar's MANIFEST.ML file named the following dependencies (and versions!):

Class-Path: protobuf-java-2.4.1.jar httpclient-4.2.2.jar httpcore-4.2.
2.jar commons-logging-1.1.1.jar commons-codec-1.6.jar

…I needed these exact file names, too. So, I downloaded the jars from http://mvnrepository.com/artifact/com.google.protobuf/protobuf-java/2.4.1 and https://hc.apache.org/downloads.cgi, placed them in the same directory as the android-checkin-1.0.jar and – out of laziness because I didn't download the correct versions – renamed them accordingly. Worked!

However, now that I have BlankStore installed, it always force closes as soon as I search for an app. I know BlankStore was discontinued but has anyone else experienced the same issue? I just entered the Android ID I generated earlier (along with my Google credentials) when I was asked for it by the BlankStore APK. Any mistakes here? The credentials are definitely correct. Also, I'm running Cyanogenmod 11 with XPrivacy installed but I enabled access to the app list and to the internet.

Logcat output:

W/dalvikvm( 6169): threadid=11: thread exiting with uncaught exception (group=0x41606ce0)
E/AndroidRuntime( 6169): FATAL EXCEPTION: AsyncTask #1
E/AndroidRuntime( 6169): Process: com.android.vending, PID: 6169
E/AndroidRuntime( 6169): java.lang.RuntimeException: An error occured while executing doInBackground()
E/AndroidRuntime( 6169):	at android.os.AsyncTask$3.done(AsyncTask.java:300)
E/AndroidRuntime( 6169):	at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
E/AndroidRuntime( 6169):	at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
E/AndroidRuntime( 6169):	at java.util.concurrent.FutureTask.run(FutureTask.java:242)
E/AndroidRuntime( 6169):	at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
E/AndroidRuntime( 6169):	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
E/AndroidRuntime( 6169):	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
E/AndroidRuntime( 6169):	at java.lang.Thread.run(Thread.java:841)
E/AndroidRuntime( 6169): Caused by: com.gc.android.market.api.LoginException: The login request used a username or password that is not recognized.
E/AndroidRuntime( 6169):	at com.gc.android.market.api.MarketSession.login(MarketSession.java:384)
E/AndroidRuntime( 6169):	at com.gc.android.market.api.MarketSession.login(MarketSession.java:334)
E/AndroidRuntime( 6169):	at com.android.vending.google.GooglePlayConnection.openConnectionSynced(GooglePlayConnection.java:131)
E/AndroidRuntime( 6169):	at com.android.vending.google.DefaultGooglePlayConnection.requestAppsSynced(DefaultGooglePlayConnection.java:309)
E/AndroidRuntime( 6169):	at com.android.vending.google.DefaultGooglePlayConnection.requestApps(DefaultGooglePlayConnection.java:302)
E/AndroidRuntime( 6169):	at com.android.vending.google.DefaultGooglePlayConnection.queryAppList(DefaultGooglePlayConnection.java:199)
E/AndroidRuntime( 6169):	at com.android.vending.tasks.AppListTask.doInBackground(AppListTask.java:62)
E/AndroidRuntime( 6169):	at com.android.vending.tasks.AppListTask.doInBackground(AppListTask.java:10)
E/AndroidRuntime( 6169):	at android.os.AsyncTask$2.call(AsyncTask.java:288)
E/AndroidRuntime( 6169):	at java.util.concurrent.FutureTask.run(FutureTask.java:237)
E/AndroidRuntime( 6169):	... 4 more
W/ActivityManager( 807): Force finishing activity com.android.vending/.BlankActivity