Zap dialtone disappears on restart

I have an ATCOM box that I have removed all of the provided .conf files and am starting again to learn with the Starfish book.

I have configured it far enough to get a dialtone on a physical phone (and a dialplan to show that it works). If I reboot the computer it continues to work, but if a do a ‘restart now’ in the CLI the dial tone disappears.

What is different about an Asterisk restart and starting the thing after a reboot?

I found this error when starting Asterisk from the console

[Aug 23 09:15:25] WARNING[190]: chan_zap.c:902 zt_open: Unable to specify channe l 1: Device or resource busy
[Aug 23 09:15:25] ERROR[190]: chan_zap.c:7225 mkintf: Unable to open channel 1: Device or resource busy

Does anyone know what might cause this?

Sorry, here are the full lines

[Aug 23 09:15:25] WARNING[190]: chan_zap.c:902 zt_open: Unable to specify channel 1: Device or resource busy
[Aug 23 09:15:25] ERROR[190]: chan_zap.c:7225 mkintf: Unable to open channel 1: Device or resource busy
here = 0, tmp->channel = 1, channel = 1
[Aug 23 09:15:25] ERROR[190]: chan_zap.c:10615 build_channels: Unable to register channel ‘1’

hello:
make sure the IRQ is ok. cat /proc/inteerupts and check the IRQ activities.