Ok.
1) the modification I've provided would not work, sorry.
2) I just installed the mod on a fresh 4images, added my modification from page 6, added Jan's modification, then fixed a few lines after Jan modification and everything was working. I can not see anything in Jan's or in my "wrong" modification that would affect your "all" link, there is not even remotely close to it.
So, here is what I'd suggest u to do:
1) replace memberlist.php with the fresh one (thats the only file needs to be adjusted)
2) add the code for alphabetic selection
3) add Jan's groups code
4) replace the following:
find: $condition = " AND ".get_user_table_field("", "user_name")." NOT REGEXP(\"^[a-zA-Z]\")";
replace it with: $condition = " AND ".get_user_table_field("u.", "user_name")." NOT REGEXP(\"^[a-zA-Z]\")";
find: $condition = ($ltr) ? " AND ".get_user_table_field("", "user_name")." LIKE '".addslashes($ltr)."%'" : "";
replace it with: $condition = ($ltr) ? " AND ".get_user_table_field("u.", "user_name")." LIKE '".addslashes($ltr)."%'" : "";
find:$user_cache = array();
replace it with:$user_cache = array(0);
find:$sql = "SELECT user_id
FROM ".GROUP_MATCH_TABLE."
WHERE group_id IN (".$show_group_id.")";
replace it with:$sql = "SELECT g.user_id
FROM ".GROUP_MATCH_TABLE." g
LEFT JOIN ".USERS_TABLE." u ON (u.user_id = g.user_id)
WHERE g.group_id IN (".$show_group_id.") ".$condition;
find: FROM ".USERS_TABLE."
WHERE user_id IN (".implode(',', $user_cache).")
ORDER BY $order_by
replace it with: FROM ".USERS_TABLE." u
WHERE u.user_id IN (".implode(',', $user_cache).")$condition
ORDER BY u.$order_by