how to get difference betwen two dates in mssql

SELECT DATEDIFF(minute,CONVERT(VARCHAR, CURRENT_TIMESTAMP, 102),convert(varchar, t.xxxxxx, 102)) AS daydifference FROM (SELECT MAX(autoid),xxxxxx FROM Xtable WHERE uid=3)t;

I am getting error at last "t". No column name was specified for column 1 of 't'.