My sort buttons are disabled also and I haven't found a way to enable them. However, I get around this by manually changing the SQL that creates the rowset. Until someone provides an answer of how to enable these buttons, you might try the following:
While viewing your table rows:
1)Click the SQL icon(in my list, about 6 icons before the sort buttons)
2)The SQL is shown such as follows:
SELECT *
FROM CORP
3)Add the following specifying the name of the column you want to sort by and whether you want it to sort ascending(ASC) or descending(DESC). Ascending is default and doesn't have to be specified
SELECT *
FROM CORP
ORDER BY ID DESC
4)Click the ! icon to execute the query and see the rows sorted in the order specified.
Hope this helps until someone can provide the exact answer you're looking for.