This message (or something like it) appears when a restart is required but can't be carried out immediately because the Humax is Recording. If the Humax is not 'busy' the Dismiss would be replaced by a 'Do a restart now - Y/N' message. The 'Dismiss' notice, I guess just takes the message off the screen
The message appears at the top of the WebIF page when an existing schedule event is modified in some way (eg change of destination folder). The CF cannot modify the schedule database while the humaxtv process is running (which is always during normal operation), so the database changes are queued until the next reboot and applied before humaxtv starts up. The warning tells you there are pending updates, the "Dismiss" option lets you acknowledge the message and hide it from cluttering up the screen.
If you schedule a new event via the EPG page a message offers you the option of forcing a restart (with the warning that the CF-triggered restart might not complete without manual intervention). You can also force a restart via the Diagnostics page.
Perhaps it would be better if the message button said "Acknowledge?".