problem with "Parameter must be a Guid ..."

Hi guys.

I'm new with scripting and Python for Grasshopper.

I'm having a problem with this code.
The message error is: "Parameter must be a Guid or string
representing a Guid"... what does it mean?
The error appears when I add the "rs.RotateObject" command;
if I comment the line the mistake disappears.
I'm waiting for your help.

Thanks