I am getting similar results with a WS-C2960-48PST-L. The switch was previously was running 15.0 and I wanted to downgrade to 12.2. I loaded the new 12.2 software and got the looping " Unexpected exception to CPUvector 1100". I have run "format flash:" and the boot process hangs after this message, "...uncompressed and installed, entry point: 0x3000 executing…". It was hung for at least 10 minutes, I didn't try letting it go longer.
I also tried " archive download-sw /force-ucode-reload" when attempting to downgrade to 12.2 and I am sure that my images were not corrupt. IE. the "verify /md5" command checked out OK.
I am now installing 15.0 via XMODEM, a slow process...
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