To expand a bit on the reply from Dennis: PPM executes a single command and waits for it to complete. An sh command that does not have a command specified as a parameter does not complete. Instead, it prompts for a command line to be entered interactively. Your sh command line is waiting for a command to be entered while PPM is waiting for the sh command to complete.
We have used a couple of methods to execute commands. One is to place the commands on the sh command as Dennis suggested. Another is to write a series of commands of commands to a file and execute the file. Scripts can also be created with the special commands ksc_begin_script and ksc_end_script.