Have you check if this is just the ssh session timing out on your remote machine?

You are calling the program with nohup, but that applies locally, doesn't it?

ssh requires that stdin, stdout, and stderr (all the stdio stuff) be associated with a valid file or device handle. When you run in the foreground, it will take these from the shell (the tty you are running on). When run in the background, there is no stdin, so in your case you will need to redirect the input. If the file "/user/tom/b.sh" is on your local machine, then try this

ssh another-machine <"/user/tom/b.sh"

in order to redirect stdin appropriately. Don't know if it will work for sure, but it should.