System stops processing inbound calls

I am not certain if this is a coincidence or what, however when I receive email from the FreePBX system that says: UPGRADE NOTICE: There are xx modules available for online upgrades, the system seems to stop processing inbound calls. You can still dial outbound and internal extensions, however inbound calls fail with CHANUNAVAIL. Even after I upgrade the modules, I still receive the same error. Rebooting the box resolves the issue. Any ideas?

Thanks