How can I use crosstab functons in PostgreSQL 9.3?

I am trying to learn about crosstab functions in ProgreSQL 9.3, but none of the examples I’ve found are working.  I get errors claiming the functions are unknown, but when I try running CREATE EXTENSION tablefunc, I am told that its methods already exist. 

For example, I am trying to run the code contained on this page: https://learnerspeak.wordpress.com/2012/09/02/97/ .  After adjusting quotation marks, my crosstab query from that example is:

SELECT *

FROM crosstab(

  $$select rowid, attribute, value

    from ct

    where attribute = 'att2' or attribute = 'att3'

    order by 1,2$$)

AS ct(row_name text, category_1 text, category_2 text, category_3 text);

That query gives me the following error message:

ERROR:  function crosstab(unknown) does not exist

LINE 2: FROM crosstab(

             ^

HINT:  No function matches the given name and argument types. You might need to add explicit type casts.

********** Error **********

ERROR: function crosstab(unknown) does not exist

SQL state: 42883

Hint: No function matches the given name and argument types. You might need to add explicit type casts.

Character: 15

I don’t know why it thinks the argument’s type is unknown.  But if I explicitly cast it to text, I get:

ERROR:  function crosstab(text) does not exist

LINE 2: FROM crosstab(

             ^

HINT:  No function matches the given name and argument types. You might need to add explicit type casts.

********** Error **********

ERROR: function crosstab(text) does not exist

SQL state: 42883

Hint: No function matches the given name and argument types. You might need to add explicit type casts.

Character: 15

Thank you for your help.

RobR