In order to use cron services and kcrontab you need to have a cron daemon installed on your system. To find out if cron is active you could do the following:
Open a terminal window (like kvt) and type the following:
ps -ax | grep cron
The output of this should look like this:
2573 p0 S 0:00 cron
2893 p3 S 0:00 grep cron
In this case a cron daemon is runnin with process ID 2573.
Note: The process ID is assigned dynamically. It will most certainly
be a different one on your system and can change (for example after a
reboot).
If there is no cron process on your system you may not have cron installed.
Please see the documentation provided by your OS Vendor. Further information
may be found by typing:
man cron
This will call the man-pages for cron. Read the information carefully.