Unable to reboot server after scan starts

We have a server with the Windows 2003 Small Business Server operating system. We run a weekly full scan starting 10:00 p.m. on Saturday which gets done about 4:00 a.m. Monday.

I needed to reboot the server in the middle of the scan on Sunday. SEP wouldn't let the server reboot. I finally took it down with the power button. How can I stop a scan that has started?

We have SEP Small Business Edition version 12.1.4013.4013.

Thanks!