The game number that has been purchased cannot be verified!

In the previous has downloaded a minecraft before, also can play the game normally, but after a few months it change to the test version on the sudden, the reason that I guess that may be is because the serial number does not give verification so will cause this situation, so I delete the previously downloaded software, intended to download again to see if it can solve the problem, the result is not! Because there must be a purchase serial number, and to verify to download the official play software, but why I was previously able to download successfully, suddenly change the trial version of the serial number can not be verified? (Serial number simen was bought at a convenience store