Rednet errors with redpower elevator control code.

I am a new member to the forum and new to the computer craft and redpower mods.

I am working on a Redpower and computer craft elevator I followed a Video on Youtube for Tekkit Elevator.

When I reboot the Motor Control Computer I get this.

Rednet 57 no open sides.

Can you please help with this?

When I go into Lua and type rednet.open("back") I get Rednet 14 Invalid Side

Split into new topic. You failed to provide a title, so one was provided for you.

Please post the full code of the program you are using.

Do you have a modem in that side?