How do I fix the licensing on Adobe Photoshop CS4?

Hey there. I just finished installing some Adobe software on my Mac. Everything went fine until I got to Photoshop. I installed Photoshop and immediately got a warning "License Expired." According to what I found online, I should simply need to set the Mac's date to 2008, delete the license, and reinstall it at the current date again. Well, that has not worked for me. Does anyone have any ideas on how to fix this? I do have a valid serial number and the installation DVD.