This is a trivial typo.
You have several lines which include:
`echo -ne '\015'\`
I presume you mean to embed a Ctrl-G bell character into the output.
The error is because you have placed an unnecessary backslash before the final backtick, thus escaping it. This isn't what you want.
`echo -ne '\015'`
Another thing: Get rid of this script entirely.
For starters, you really shouldn't be rebooting your server via a cron job. If you think you want to, you have another problem, which you should actually find and fix. Any reasonable server should be able to remain up and running for more than a day without intervention.
shutdown command will happily alert all logged on users (and screen sessions!) automatically. If you really must reboot, try using it to schedule your reboot.