The above errors can be caused by 5 reasons.
1. The user 'nobody' entry in /etc/cron.deny file.
Try looking in the /etc/cron.deny file for the user 'nobody' and remove it.
2. You have an open_basedir restriction on your domain.
Ask your system adminstrator to remove that restriction by editing the php.ini file. ( In case of plesk, you need to turn off open_basedir restriction in customised httpd include file for your domain.)
3. CE looks for the php binary in /usr/local/bin/php and /usr/bin/php and your system might have it elsewhere.
Ask your system administrator to create a symlink in any of those places, pointing to the actual location.
4. The user under which your web server is running doesn't have execution permissions on the php binary file in any one of those locations.
Ask your system administrator to grant the appropiate access. To find out what user is this, while logged into CE as an administrator in your installation, point your browser to newedge/diagnostics/phpinfo.php and look for the entry "User/Group" in the screen (this URL applies only for versions 3 and up).
5. PHP safe_mode may be On for the domain.
Turn off safe_mode for the domain.
Try all the above fixes for the specified error.