Never seen anything like that.
SELECT * FROM LeadTable
WHERE Operator = '$CurrentOp'
AND CallBackDateTime IS NULL
AND (LeadDisposition IS NULL OR LeadDisposition = 'NA' OR LeadDisposition = 'LM')
ORDER BY DispositionDateTime ASC, TimesDispositioned ASC, LeadType ASC
Is it possible there is no record that satisfies all three AND'ed conditions???
You could rewrite the last of those:
AND IFNULL(LeadDisposition,'NA") IN ('NA','LM')
I don't see why that would matter, but worth a shot.