Invalid Receipt Error on Mac

Q. I received this error, "Invalid Receipt. The receipt is invalid (2)." What do I do?

A. We'll need to make sure that the computer's clock is synchronized with an appropriate time server. Here's how:

1. Open System preferences
2. Click on “Date & Time”
3. If the lock on the bottom left is locked, click on it to unlock, you may be asked to enter your computers' password
4. At the top you should see a checkbox saying “Set date and time automatically”, if the checkbox is unchecked, click it to make it checked, if the checkbox is checked, uncheck it by clicking once and then check it again to check it.
5. Make sure that in the field next to the checkbox it has the appropriate apple server for your location (Apple Europe (time.euro.apple.com.), Apple Americas/U.S. (time.apple.com.) or Apple Asia (time.asia.apple.com.), if the wrong server is selected, click the popup arrow on the right to choose the right server.
6. Close the System Preferences window
7. Try to activate again