This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
"./script.ksh" means "the file in the current directory named script.ksh". When you run your script from cron, the current directory is generally going to be your home directory, so unless script.ksh is there, this isn't going to work. There are many ways to deal with this; one simple one would just be to use an absolute path (i.e., like "/home/Srivastava/bin/script.ksh").