Para concatenar números en MSSQL-2005 debe usar CAST
CAST(loginsFailed AS VARCHAR(10)) + '/' + CAST(LoginCount AS VARCHAR(10))
loginsFailed y loginCount arriba es en realidad su select count distinct
fragmentos
Espero que esto funcione
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))