将varchar值转换为数据类型int时，SQL转换失败

I have this query:

我有这个问题:

SELECT C.CustomerID, 
       Q.Question_ID, 
       Q.Department,  
       C.DueDate  
FROM homefront.dbo.TPM_Questions_Default AS Q  
LEFT OUTER JOIN homefront.dbo.CustomerQuestions AS C 
    ON Q.Question_ID = C.QuestionID 
INNER JOIN tblCustomers T 
    ON CONVERT(INT, CONVERT(VARCHAR(MAX), T.Customer_No )) = C.CustomerID 
WHERE C.DueDate <= GETDATE() AND C.DateCompleted IS NOT NULL
SELECT C.Custome