Which profile did you use?
There may not be enough free space for virtual memory swapfiles to be created. You could try booting in verbose mode by holding down Command V at the start of the attempt to boot from the flash drive, and compare the messages seen onscreen to those you get if you perform a verbose boot from your usual startup volume. If looking at the onscreen messages during the boot does not give you a hint about why the boot is not work, please send a message to
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, including a link to this thread. You will receive a reply by email tomorrow, and may be asked to send in an Apple System Profiler Report. Thank you.
If you have another flash drive, preferably a larger one, please try it. There are some USB devices that are not bootable.