My mbp shipped with OS 10.8, and I had upgraded twice to 10.10
I've a 10.7 USB which upgraded my old MBP.
My plan today was to boot with my new ssd, my time machine back up and the Lion usb plugged in.
I would then click on the Lion usb, and tell it to put the OS and time machine back up on the ssd.
So I help down ALT and when it started it gave me the options of the usual Mac internal or the Lion USB.
I clicked Lion, but instead of taking me to the install options (Disk utility, restore from time machine etc etc) it gave me that grey circle with a diagonal line through it. The no entry sign - grey on grey - that I think you have.
Some googling said that it is because I was trying to usb a 10.7 install on a MBP that shipped 10.8
You can't go back, apparently.
So if any of the OSs are older than the mac you got, you will get this error. The grey in grey no entry.
I just cloned my HDD to my ssd (Carbon copy cloner free 30 day trial) using an external stat-usb3 wire and all is good.
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