Each time you install a free update for perpetual Articulate products, such as Storyline 3 and Studio '13, you'll be prompted to re-activate your software. This is normal behavior. The good news is that the software remembers your serial number so you just have to click Activate to complete the process.
Note: Security restrictions on some computers or networks could prevent Articulate software from seeing the serial number stored in your computer's registry. If your serial number is missing from the activation form after updating your software, copy and paste it from your purchase confirmation email. Let us know if you need help!