Conversion failed when converting the varchar value 'TerminatedByCompany' to data type int
I am not entirely sure what you are trying to achieve by joining on t.Name and u.EmploymentStatusId as they are different data types, varchar and int. When this join is being completed it is trying to implicitly convert t.Name into an int and it contains data that cannot be converted as the error message shows.

If you are trying to get the employment status of the user with CustomerId of 214 I would do something similar to:

 SELECT
 t.Name AS Status

 FROM 
 dbo.Paychecks AS p INNER JOIN dbo.Users AS u ON u.Id=p.UserId 
 INNER JOIN dbo.TerminationReasons AS t ON t.Id = u.EmploymentStatusId
 WHERE u.CustomerId=214 order by u.FirstName;


If I have missed the point please clarify exactly what you are trying to achieve.