Trying to solve a SocketError [Errno 13] Permission with PL/Python in PostgreSQL 9.3

Regards to all the list.
First all the info about the system:

O.S: CentOS 7 64 bits
PostgreSQL version:

SELECT version();
version
--------------------------------------------------------------------------------------------------------------
  PostgreSQL 9.2.7 on x86_64-redhat-linux-gnu, compiled by gcc (GCC)
4.8.2 20140120 (Red Hat 4.8.2-16), 64-bit
(1 row)

Neo4j version: 2.1.M
Py2neo version: 2.0.8
Python version:
python
Python 2.7.5 (default, Jun 17 2014, 18:11:42)
[GCC 4.8.2 20140120 (Red Hat 4.8.2-16)] on linux2

Now the problem:

We are working here to integrate PostgreSQL with Neo4j through PL/Python
using the py2neo module for it, and when we want to send sentences to
Neo4j using port 7474, the executed code raises a SocketError [Errno 13]
Permission denied.

I tested the same code in a normal python script outside of PostgreSQL,
and it works well, but the problem is when I use the code inside
PostgreSQL with PL/Python.
This is the code of a simple function to search a node in the Neo4j graph:

CREATE OR REPLACE FUNCTION search_professor_node(nombre_prof text)
   RETURNS text AS
$BODY$
from py2neo import Graph
from py2neo.cypher import CypherTransaction

graph = Graph("http://neo4j:neo4j@10.8.45.136:37474/db/data")
tx = graph.cypher.begin()
statement = "MATCH (pf:Professor) WHERE pf.nombre = {name} RETURN pf;" ,
tx.append(statement, parameters={'name': nombre_prof})
professor= tx.commit()
$BODY$
   LANGUAGE plpythonu VOLATILE
   COST 100;

and it can be used:
SELECT search_professor_node('Max');

The completed error is:

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

ERROR: py2neo.packages.httpstream.http.SocketError: Permission denied
SQL state: XX000
Context: Traceback (most recent call last):
   PL/Python function "search_professor_node", line 6, in <module>
     tx = graph.cypher.begin()
   PL/Python function "search_professor_node", line 666, in cypher
   PL/Python function "search_professor_node", line 212, in metadata
   PL/Python function "search_professor_node", line 257, in get
   PL/Python function "search_professor_node", line 965, in get
   PL/Python function "search_professor_node", line 942, in __get_or_head
   PL/Python function "search_professor_node", line 432, in submit
   PL/Python function "search_professor_node", line 361, in submit
PL/Python function "search_professor_node"

Thanks a lot for your time, and I hope to find a suitable solution for it.