<>false is actually a TRUE.
maybe you should not use prebuilt queries that check for NULL,and instead, build it on the fly,
and ignore fields that are null. (you see the trouble that does)
Code:
'----------------
sub btnReport_click()
'----------------
dim sWhere as string
dim qdf as querydef
sWhere = "(1=1)"
if not IsNUll(cboCat) then sWhere = sWhere & " and [State]='" & cboCat & "'"
if not IsNUll(cboOffNum) then sWhere = sWhere & " and [officenum]='" & cboOffNum & "'"
docmd.OPenReport "rMyReport",acViewPreview,,sWhere
'or build the query behind the report
set qdf = currentdb.querydefs("qsMyQuery")
qdf.sql = "select * from table where " & sWhere
qdf.close
docmd.OPenReport "rMyReport",acViewPreview
end sub