FCE 4.0.1 Serial Number Help!

I recently did a software update on my Final Cut Express 4.0 software to 4.0.1 and now licensing is asking for a serial number before I can get into the application. I have a Drama Major Work due soon and I really need to get into my editing!! Can anyone help me with the Serial Number? Where do I find it seeing as I updated it, I didn't buy it as 4.0.1 so it cant be on a box?!