SELECT logcount, logUserID, maxlogtm , DATEDIFF(day, maxlogtm, GETDATE()) AS daysdiff FROM statslogsummary WHERE daysdiff > 120
I get
How about using a subquery(this worked for me in Mysql)?
SELECT * from (SELECT logcount, logUserID, maxlogtm , DATEDIFF(day, maxlogtm, GETDATE()) AS daysdiff FROM statslogsummary) as 'your_alias' WHERE daysdiff > 120