Android in-app billing problem

I tried out Google's example Dungeon application to buy an item i have uploaded the signed apk on my developer account. I downloaded it from the market and when i try to buy the sword item it says on the screen,

sword_001: request purchase reeturned RESULT_ERROR

Which wasn't very descriptive.

Even though I had already put the item up on the application on my developer console, and it showed the billing screen and i clicked buy item but that error appeared.

On close inspection on the logcat i found this string. I still have no clue how to fix this

05-12 20:28:31.695: DEBUG/vending(1922): 开发者_运维百科[102] BaseAction.run(): ApiException: com.android.vending.api.ApiException: Error from backend. Request=com.android.vending.model.PurchaseOrderRequest, Response=INTERNAL_SERVICE_ERROR

Your suppose to add the sword_001 as a product list in your market account

please used this link https://github.com/robotmedia/AndroidBillingLibrary/ this is very useful for you.and android-billing library is also good working.i implement this library in my project work well try it.