When you install Expressor it does not alter the environment, which means that the Expressor directories are not put onto the path. Consequently, a regular command window does not have the information needed to run a dataflow. The Expressor.Launcher.exe utility sets the environment.
See the knowledge base article on running Expressor from Windows scheduler. This discusses how to use Expressor.Launcher.exe to run a dataflow from another process.
Alternatively, examine the path in an Expressor command window and note all the Expressor directories. Then modify the path entry on your computer to include these directories. Once you do this, there is no need to set the environment using Expressor.Launcher.exe.