http://www.w3schools.com/sql/sql_groupby.asp
the syntax seems right. I think the problem is that you have values of 'argument' like:
argument
xxx
yyy
yyy
zzz
zzz
zzz
zzz
is what you're wanting a count of where argument = zzz?
then you'll need to cycle through your recordset to get there, because the first value in the recordset will be '1' (from xxx), then '2' (from yyy) then '4' which is what you want...
try tacking "WHERE argument = 'zzz'" on the end there... or actually, replace the groupby with that: it'll give you the count of the specific group you want...