error creating yosemite boot disk

Thanks Worked Great!!

Apple has a page dedicated to this:-

Create a bootable installer for OS X - Apple Support

I wanted a boot disk for Yosemite 10.10.5 which I currently have, before I upgrade to El Capitan, just in case I don't like the upgrade. I used the instructions in "How to install OS X on an external drive connected to your Mac". The directions are clear and don't involve command line use.

I purchased a 32 GB !!! USB 3 stick and carefully erased and formatted it as per instructions. I originally had created two partitions with 10.2 GB allocated for the OS X download, but it said it wanted about 10.5 so I made the USB stick one partition and made all 30 GB available so it would have PLENTY of room. Numerous tries at download hung up with about 15 min remaining.

Solution: I uninstalled Malware Bites anti-malware program. First try after that went flawlessly

Side note: my iMac was not purchased from Apple, and came pre-loaded with Yosemite. So I could not go to the App store and get to a record of my "purchase" of Yosemite. And by now they only offer El Capitan to download. The above procedure allows for authentication using your computer's serial number sent to Apple during the Install from OS X recovery.

Hope this helps someone.

Thank you. It was my case too. Problème résolu! ^^