Encountered with 6.1 (but that's not in the category-dropdown here at Sourceforge)
Somehow accidentally a target-group that was already in use for a while got modified so that it did not contain any rule at all. Using that target-group then lead to problems in at least two cases:
* trying to send a mailing to that target-group it failed with an SQL-error:
ERROR: Resource key "SQL-Error:
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error
in your SQL syntax; check the manual that corresponds to your MySQL server
version for the right syntax to use near ') AND bind.user_status=1 GROUP BY
bind.mediatype, cust.mailtype' at line 1" not found in default bundle
SQL-statement that triggered this was:
SELECT count(*), bind.mediatype, cust.mailtype FROM customer_1_tbl cust, customer_1_binding_tbl bind WHERE bind.mailinglist_id=1 AND cust.customer_id=bind.customer_id AND () AND bind.user_status=1 GROUP BY bind.mediatype, cust.mailtype
The brackets in the last part are correct since a target-group is used for which the SQL-part is fetched - but that one is empty since it didn't contain any rule at all.
* trying to "Show recipients" in the backend, selecting the target-group and clicking on "update" you get a permanent error (I guess since an SQL fails again somewhere) - and you can't go back to the list anymore, since all you do in "show recipients" always uses the current selection (and you can't reset it). Only way is to logout/login to get a new session.