Your PATH is setup differently when your shell is interactive (= when you are logged in on the server), and when not interactive (running commands with ssh).
Look into the rc files used by your shell, for example .bashrc, .bash_profile, .profile (depends on your system). If you set PATH at the right place, then ttisql can work when you run it via ssh.
Another solution is to use the absolute path of ttisql, then it will not depend on your PATH setup.