A family of Microsoft relational database management systems designed for ease of use.
I may be overlooking something, but it seems the SQL order of statements is incorrect. GROUP should be after WHERE
SELECT EmployeeID, Sum(Attendance.VacHrs) AS TotalHrs
FROM Attendance
GROUP BY EmployeeID
WHERE DateAbsent Between Forms!StartEnd!txtStart AND Forms!StartEnd!txtEnd;
Proper order would be
SELECT column_name(s)
FROM table_name
WHERE condition
GROUP BY column_name(s)
ORDER BY column_name(s);