x=var('x') - getting TypeError: cannot perform reduce with flexible type

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I just installed Sage 5.12 under Mac OSX 10.9 (Mavericks). I started the notebook and then proceeded to work through the "Getting started" document. In Chapter One, the first page there is an example of Symbolic programming. It starts with:

x=var('x')

When I evaluate this I get the following error:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "_sage_input_16.py", line 10, in <module>
    exec compile(u'open("___code___.py","w").write("# -*- coding: utf-8 -*-\\n" + _support_.preparse_worksheet_cell(base64.b64decode("eD12YXIoJ3gnKQ=="),globals())+"\\n"); execfile(os.path.abspath("___code___.py"))
  File "", line 1, in <module>

  File "/private/var/folders/k_/vvbn4jxs6jx2z21s7xdj088c0000gq/T/tmpZ3Z0gy/___code___.py", line 2, in <module>
    exec compile(u"x=var('x')" + '\n', '', 'single')
  File "", line 1, in <module>

  File "/Applications/Sage-5.12-OSX-64bit-10.8.app/Contents/Resources/sage/local/lib/python2.7/site-packages/numpy/core/fromnumeric.py", line 2693, in var
    keepdims=keepdims)
  File "/Applications/Sage-5.12-OSX-64bit-10.8.app/Contents/Resources/sage/local/lib/python2.7/site-packages/numpy/core/_methods.py", line 68, in _var
    arrmean = um.add.reduce(arr, axis=axis, dtype=dtype, keepdims=True)
TypeError: cannot perform reduce with flexible type

DOES ANYONE KNOW WHAT IS WRONG WITH THIS?

If I try this from the SAGE command line (as opposed to the notebook) it appears to work. Am I doing something fundamentally wrong by using the notebook for this?

It is Sage's own introductory example, and it is not working! It is the first thing I tried, so it does not give one confidence with the system.

The error appears to be emanating from it's own internal version of Python.

Thanks in advance for any help.

Regards.

Bob