Logic won't install- "invalid serial number" message

I've made several attempts to install Logic 8 on my Mac from that era, but I get no farther than the window to enter the serial number, as I am always met with the "invalid serial number" message. I purchased the software a number of years ago, and haven't had the occasion to use it until recently. Still, it would be helpful to be able to install the program. Otherwise, I'll just have to make the project work with my Adobe software. Any advice?