sub query

Hi I have this problem, when I try to run this query:

SELECT MAX(d), host_position FROM (SELECT host_position, 
COUNT(host_position) as d FROM sss_host GROUP BY host_position) as e;

am getting and ERROR: Attribute e.host_position must be GROUPed or used in 
an aggregate function.

Please to advice what could be the problem and how can I rewrite it to work 
thanks in advance.

Kind regards
+-----------------------------------------------------+
| Martin W. Kuria (Mr.) martin.kuria@unon.org
+----------------------------------------------------+

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