Your Owner Name on your device must match with the Owner Name you registered with when you received your registration key (unlock code). For example. If you registered with "John Doe" then you got a key "ABCD1234".
Make sure the Owner Name on your device is "John Doe" with not extra spaces and symbols. Then the registration key should work. To check your Owner Name, tap on START > SETTINGS > OWNER INFORMATION.
If the key continue not to work, it maybe that it is in cached. To clear the cache, type in another owner name and just type in random numbers to get the registration key ERROR message. Once this is done, go back and retype your original Owner Name and use the key.
If this fails, that means you do not have the correct registration key that matches your Owner Name. Contact Socket Support!
Good luck!
Socket Mobile Online Technical Support