You don't generally need to hacktivate any iPad cellular device. Simply insert any valid carrier SIM card (it does not need to be active), and the device will activate. If the device is carrier locked, it needs to be a SIM for that carrier. It is not currently possible to unlock a locked iPad4 via jailbreaking.
Then you are not talking about "Hactivating". That is a specific term relevant to devices with a cellular radio.
You are probably talking about getting valid signatures for the firmware install from Apple. This is likely because you have used TinyUmbrealla or redirected your hosts file.
Is the the setup wizard which is failing to complete? Please post a detailed and exact copy of the error message you are receiving and what the screen prompts say directly before and after you receive the error. What you are describing does not make much sense to me