Problem with nullable types in Biztalk

similar problem to someone else too..

In the Expression Editor I am unable to assign a value to a object that is
System.Nullable`1. For example, when attempting to assign a DateTime to the
object, I get the message “cannot implictly convert type ‘System.DateTime’
to ‘System.Nullable`1′”. Of course, I can not cast it, either.

How do you deal with Nullable message propertiesin BizTalk 2009

Thanks

AK