Getting "invalid command error" when giving command to CLI interface

Hello,
I have written a script in which I am telnetting from system1 to system2. There from system2 I am doing ssh to system3. This system3 is a Embedded Board running Linux.Here on system3 I am executing a code that gives me a CLI interface. In this CLI we have almost 15 commands.When we enter "show" it shows all the commands. The first(#1) command on this list is "capabilities".This command is getting executed successfully but when I try running any other commans then it says "Invalid Command". Why so ?????

Please help, I novice in Python

Thanks in advance