I was not sure whether to post this under MacbookPro, Lion, or Idiot. I have a 27inch imac running now in Yosemite. I have been an apple user since 2007. With the Yosemite upgrade I lost the use of AdobeGoLive the app I built my website with. With the thought that I might buy a Laptop regress the OS to Snow Leopard and continue in my comfort zone. I purchased a MacBookPro running Lion. I cleared out the Lion and to complete the action slapped in the disc received with my iMac all those years ago. OK cut a long story short I loaded the Apps disk instead of the OS X install disc and now Disc utility won't let me erase the apps install disc. It starts to erase then as it shows "mounting Disc" it drops out. Any sensible advice as to how to proceed would be a kindness!