MVC Data Model Validation DateTime with FoolProf

Question

I am validating two dates. I am using FoolProf to validate One date in Greater than the other like this...

[DataType(DataType.Date)]
public System.DateTime StartDate{ get; set; }

[DataType(DataType.Date)]
[GreaterThan("StartDate")]
public System.DateTime EndDate { get; set; }

The Problem I found is that it is validating other way round.

When I set a StartDate smaller than EndDate, the message it appears it

StartDate can not be greatest than End Date...

And when I set a EndDate bigger than StartDate, no message appears.

What I am missing.?

Thanks