[Python] Matplotlib pyplot.title(string) returns error

When I call pyplot.title('some string') it throws the exception, 'str' object is not callable'. I copied the following from the matplotlib online documentation:

mu, sigma = 100, 15
x = mu + sigma * np.random.randn(10000)

# the histogram of the data
n, bins, patches = plt.hist(x, 50, normed=1, facecolor='g', alpha=0.75)


plt.xlabel('Smarts')
plt.ylabel('Probability')
plt.title('Histogram of IQ')
plt.text(60, .025, r'$\mu=100,\ \sigma=15$')
plt.axis([40, 160, 0, 0.03])
plt.grid(True)
plt.show()


and get

TypeError Traceback (most recent call last)
<ipython-input-158-40fe7a831b06> in <module>()
8 plt.xlabel('Smarts')
9 plt.ylabel('Probability')
---> 10 plt.title('Histogram of IQ')
11 plt.text(60, .025, r'$\mu=100,\ \sigma=15$')
12 plt.axis([40, 160, 0, 0.03])

TypeError: 'str' object is not callable


pyplot.suptitle() works OK

I'm using python 2.7.5 and the latest release of matplotlib on an iMac with an I7 processor OSX 10.8 and 8 gig ram and ipython notebook.

Does anyone know what's going on?

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