Problem with MONTH() function

[Sebastian]

I have a query that runs perfectly when doing a date equal comparison
(see last line in the subquery: AND T2.DQ_DAT = '14.02.2005').

A direct comparison of the date is not sufficient for my needs, so I
tried to convert the date using the MONTH() function: (AND
MONTH(T2.DQ_DAT ) = 2)

When I try to run this modified query, the query won't run anymore and
hangs up.

Any suggestions?
Please see the query below.
SELECT
T1.DQ_ID,
T1.DQ_DAT,
T1.PROFIT_CENTE R_L,
COUNT(BUSINESS_ REF) COUNT,
'Not cleaned up' ENTRY_TYPE
FROM SSRP1PP.TIUFDQ0 2_REP_DATA T1

WHERE DQ_ID = 'IUF0105'
AND T1.DQ_TYP = 'M'
AND T1.DQ_DAT = '31.01.2005'
AND EXISTS (SELECT ''
FROM SSRP1PP.TIUFDQ0 2_REP_DATA T2
WHERE T1.DQ_ID = T2.DQ_ID
AND T1.DQ_TYP = T2.DQ_TYP
AND T1.TREATY_REF = T2.TREATY_REF
AND T1.OPTION_REF = T2.OPTION_REF
AND T1.BUSINESS_REF = T2.BUSINESS_REF
AND T1.BUSVAR = T2.BUSVAR
AND IFNULL(T1.SEQ,9 9) = IFNULL(T2.SEQ,9 9)
AND T2.DQ_DAT = '14.02.2005'
)
GROUP BY
T1.DQ_ID,
T1.DQ_DAT,
T1.PROFIT_CENTE R_L