Many thanks for the assistance mwillems - greatly appreciated.
I was interested in the subsequent comment about systemd but I'm sticking to your original diagnostics regarding crontab.
crontab -l opens the file where I entered * * * * * /etc/MC21start.sh > /dev/null. It is the only active line in that file.
sudo crontab -l gives a no crontab for root message
cat /etc/MC21start.sh displays its contents as follows:
export USER=pi
ps -e | grep x11vnc || x11vnc :0 -localhost -geometry 1920x1080
export DISPLAY=':0'
ps -e | grep mediacenter || mediacenter22 /mediaserver
Your ls command modified to ls -la /etc contains the line:
-rw-r--r-- 1 root root 154 Sep 7 11:02 MC21start.sh
I am assuming that this is the line that might help but I could be wrong.
The file names and locations above are different to yours as originally I followed Hilton's instructions for RDP.
Apologies for the mash up of file names etc using both "21" and "22" - it's because I upgraded from 21 to 22 in the middle of this forum exchange.
Ok I've identified a few issues. You put the script in an unusual location (/etc), instead of in the /home/pi directory. By itself that's not necessarily an issue, but items in /etc have different default permissions (umask) than items in user's home directories, and however you put it there the permissions are not currently correct. You might've skipped the chmod line in the intstructions? In any case, the script is currently not executable for any user and is owned by root, so no one can run the script at all right now, and your user doubly can't run it.
I'd advise moving it or recreating it in your /home/pi directory for tidiness, reassigning ownership to your user (chown) and fixing the permissions (chmod). It would probably be easiest to start over with the directions in the quick start guide, but if you want the absolute quickest fix, just chmod the script to 777, i.e. something like
sudo chmod 777 /etc/MC21start.sh
That will mark it as executable for all users and should allow the crontab entry to execute. Another thing to make sure of: if you're not using x11vnc, be sure to remove that line. If you are using x11vnc, no worries.