Increment Number Problem

[Debbie37]

Hi, I am trying to get a row number for each record in a group using MD_ID and CreateDate (date/time). For some MD_ID groups it works and others it does not. Can anyone tell me what I am doing wrong? Thanks in advance!

SELECT A.MD_ID, A.CreateDate, Count(*) AS [DefCt]
FROM tblAll AS A INNER JOIN tblAll AS B ON A.MD_ID = B.MD_ID and A.CreateDate > B.CreateDate
GROUP BY A.MD_ID, A.CreateDate;

Results
The last colimn is the DefCt that increments...
MD_ID CreateDate DefCt
2161 06/01/2012 15:13:00 1
2161 06/04/2012 10:55:00 2
2161 06/04/2012 13:25:00 3
2161 06/04/2012 13:43:00 4
2161 06/04/2012 13:45:00 10
2161 06/06/2012 07:47:00 7
2161 06/06/2012 08:47:00 8
2161 06/06/2012 14:28:00 9
2161 06/06/2012 14:34:00 10
2161 06/06/2012 15:08:00 11
2179 02/02/2011 15:04:00 1
2179 02/02/2011 15:05:00 2
2179 02/09/2011 08:21:00 3
2179 02/09/2011 08:27:00 4
2179 07/01/2011 12:57:00 5
2179 07/06/2011 08:12:00 6