HP-UX

So should i change to use Bourne Shell ? how to fix the warning message ?

Thanks

You don't need to fix it.
It's simply a warning which warns you that your shell code will be executed with /usr/bin/sh, since shell diferences can make your code not work as expected or at all.

If you want to use different shell in your cron, all you need to do is put a magic cookie as first line of the script you are using.
So if you want bash, you put #!/usr/bin/bash in as the first line so your shell code will be executed with bash shell.

I would advise against changing default cron shell.

Thank you all for your advice and answers.