In app billing item not found error?

I have been trying to implement in app billing of google play to my app. I am trying to implementing the sample application and test it. I have followed all the procedures which is in http://developer.android.com/guide/google/play/billing/billing_integrate.html but still i am not able to purchase any product or the subscription from the market.And my response look like below

09-17 19:38:31.902: E/Volley(4314): [444] BasicNetwork.performRequest: Unexpected response code 500 for https://android.clients.google.com/fdfe/details?doc=subs:com.product.android.dungeons:subscription_monthly

Can any one please help me in this it breaking my head fro past one week.

The in-app billing system is very fragile, which is why a lot of people will recommend you use the AndroidBillingLibrary. Beyond that, here are a few things you should check:

• Did you create your item in the dev console?
• Is the id for your item the same in the dev console and in your app?
• Is your item published?
• Have you waited at least a few hours since you published your item?
• Are you using a different Google account than your dev account to make the purchase?
• Are you testing on a real device, rather than the emulator?
• Are you using a signed APK?

If any of these questions is answered with a "no", you probably need to fix that.