Whats wrong with my union query? Its not very long... Getting error, "The expression is typed incorrectly, or is too complex to be evaluated..."

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1rst EXAMPLE:
**************************************
 
SELECT DeptName, sum(ThisMonthRec) AS ReceivedThisMonth, sum(RollingAvg) AS RollingAverage, sum(YearToDatTtl) AS YearToDateRec
FROM 
 
(SELECT
request_dept_nm AS DeptName, 
Count(request_dept_nm) AS ThisMonthRec,
NULL AS RollingAvg,
NULL AS YearToDatTtl
FROM request_fact
WHERE requested_dt BETWEEN Forms!frmRSS_TtlsByFrq!cmbMonthBeg AND Forms!frmRSS_TtlsByFrq!cmbMonthEnd
GROUP BY request_dept_nm
 
UNION ALL
 
SELECT
request_dept_nm AS DeptName, 
NULL AS ThisMonthRec,
Round((Count(request_dept_nm))/12) As RollingAvg,
NULL AS YearToDatTtl
FROM request_fact
WHERE requested_dt  BETWEEN  DateDiff("m", -12, Forms!frmRSS_TtlsByFrq!cmbMonthEnd) AND  Forms!frmRSS_TtlsByFrq!cmbMonthEnd
GROUP BY request_dept_nm)
 
GROUP BY DeptName;
 
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2nd EXAMPLE:
**************************************
SELECT DeptName, sum(ThisMonthRec) AS ReceivedThisMonth, sum(RollingAvg) AS RollingAverage, sum(YearToDatTtl) AS YearToDateRec
FROM 
 
(SELECT
request_dept_nm AS DeptName, 
Count(request_dept_nm) AS ThisMonthRec,
NULL AS RollingAvg,
NULL AS YearToDatTtl
FROM request_fact
WHERE requested_dt BETWEEN Forms!frmRSS_TtlsByFrq!cmbMonthBeg AND Forms!frmRSS_TtlsByFrq!cmbMonthEnd
GROUP BY request_dept_nm
 
UNION ALL
 
SELECT
request_dept_nm AS DeptName, 
NULL AS ThisMonthRec,
Round((Count(request_dept_nm))/12) As RollingAvg,
NULL AS YearToDatTtl
FROM request_fact
WHERE requested_dt  BETWEEN  DateDiff("m", -12, Forms!frmRSS_TtlsByFrq!cmbMonthEnd) AND  Forms!frmRSS_TtlsByFrq!cmbMonthEnd
GROUP BY request_dept_nm
 
 
UNION ALL
 
SELECT
request_dept_nm AS DeptName, 
NULL AS ThisMonthRec,
NULL As RollingAvg,
Count(request_dept_nm) As YearToDatTtl
FROM request_fact
WHERE requested_dt BETWEEN #06/01/2008# AND #06/30/2008#
GROUP BY request_dept_nm)
 
GROUP BY DeptName;