This is where Analysis Services date attributes are incompatible with SQL DATETIME data type. You will need to create a calculated field on your Orders table view inside Analysis services and use CONVERT to convert your real date to a date Analysis services will understand when linking to your date dimension.
Example calculated field.
CONVERT(DATETIME, datename(dd, orderdate) + '/' + datename(mm, orderdate) + '/' + datename(yy, orderdate), 3)
You should then be able to link your time dimension via the new calculated field