That error can really only come up form a few things. If the program does not exist, if it's typed wrong, or if the computer can't find it.
Since it works when you run it manually, the program is there. So something is happening when you are running it from the original batch file so it can't find the command. If you put in the full path to it in the second batch file, that should fix it. Make sure you use quotes if the program path has spaces or the short directory names.
Or make the schtasks command part of the first batch file, see if that runs OK.