Error plotting root systems in Sage

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I am trying to use the Sage package for root systems, but it keeps returning an error. Here is what I am trying to do in the Notebook of Sage 5.7: I enter exactly the following lines from the tutorial for visualizing root systems

sage: L = RootSystem(["A",2]).ambient_space()

sage: L.plot()

The output I get is a traceback ending in 'unsupported operand parent(s) for '*': Full matrix Space of 2 by 2 dense matrices over real field with 53 bits of precision and vector space of dimension 3 over rational field'

I do not understand what I am doing wrong and what this message means. I am a newcomer to sage and all I want is to print a root system with some weights added for illustration purposes. I would appreciate any pointers.