За свързване на числа в MSSQL-2005 трябва да използвате CAST
CAST(loginsFailed AS VARCHAR(10)) + '/' + CAST(LoginCount AS VARCHAR(10))
loginsFailed и loginCount по-горе всъщност е вашият select count distinct
фрагменти
Надявам се, че това работи
CAST ((SELECT COUNT(DISTINCT loginsFailed) FROM users WHERE users.employeedID = userDetails.employeeID AND users.startdate = 01-01-2013) AS VARCHAR(10))
+ '/' +
CAST ((SELECT COUNT(DISTINCT logins) FROM users WHERE users.employeedID = userDetails.employeeID AND users.startdate = 01-01-2013) AS VARCHAR(10))