$nohup ./rmanbkp.sh
nohup: cannot run command ‘./rmanbkp.sh’: Permission denied

$chmod +x rmanbkp.sh
$nohup ./rmanbkp.sh
nohup: appending output to ‘nohup.out’
nohup: cannot run command ‘./rmanbkp.sh’: No such file or directory

The first line in rmanbkp.sh was

#!/usr/bin/sh

It might be a shell problem. Check ksh path

$which ksh
/bin/ksh

Change it to

#!/bin/ksh

Or, it might be a path problem. Check sh path

$which sh
/bin/sh

Change it to

#!/bin/sh

Reference:

1. http://docs.jach.hawaii.edu/JAC/JACUN/008.0/node42.html
2. http://www.gammon.com.au/forum/?id=8009&page=1