[kgroneman]

First of all THANK YOU so much for your time and effort helping me. I don't know much of anything about SQL queries. I tried your suggestion and got a timestamp error, so I changed the syntax of the date line, with the same error:

SELECT count(vb_post.postid) AS vb_postcount, vb_user.username
FROM vb_post AS vb_post
LEFT JOIN vb_user AS vb_user ON (vb_user.userid = vb_post.userid)
LEFT JOIN vb_thread AS vb_thread ON (vb_thread.threadid = vb_post.threadid) 
WHERE dateline > UNIX_TIMESTAMP('2016-03-31') AND vb_post.dateline < UNIX_TIMESTAMP('2016-05-01')
AND vb_thread.forumid NOT IN (10,588,589,591,592,593,594,595,597,599,601,608,609,641,644,645,646,647,649,650,652,654,671,689,737,739,740,741,782,783,1228,1229,1230,1231,1232,1233,1234,1235,1236,1237,1239,1240,1241,1242,1274,1275,1278,1279,1280,1289,1290,1292)
GROUP BY vb_post.userid
ORDER BY vb_postcount
DESC

The error is:

An error occurred while attempting to execute your query. The following information was returned. 
error number: 1052 
error desc: Column 'dateline' in where clause is ambiguous

So for some reason, making the changes you suggested changed the way it reads the date, and I'm not nearly smart enough to figure out why. :-\