The conversion of a varchar data type to a datetime data type resulted in an out-of-range value.

Environment: SQL Server 2008 R2
Problem: An error message occurred "The conversion of a varchar data type to a datetime data type resulted in an out-of-range value", when I was trying to flag invalid date.

The following data are stored in the order_dt

order_dt
Apr  3 2013 12:00AM
20130229
Apr  3 2013 12:00AM

Code:

SELECT 
CASE WHEN order_dt >= getdate() THEN 'date leap'
WHEN ISDATE(order_dt) = 0 THEN 'invalid date' END AS 'Date'
FROM StagingTable