Trying To Compare LINQ-to-Entity To Date Results In Error

I have a simple If..Then like so:

If rhcexists.First.SignatureDate > Date.Today.AddMonths(-6) Then
End If

rhcexists is a simple query to the Entity Model:

Dim rhcexists = From p In dbContracts.Signatures _
Where p.StudentID = CStr(Session("people_code_id")) _
And p.ContractType = "rhc" _
Order By p.ID Descending _
Select p

Problem is that this comparison results in an error:

LINQ to Entities does not recognize the method 'System.Object get_Item(System.String)' method, and this method cannot be translated into a store expression.

This is occurring on the If clause. Any ideas why this occurring and how I can fix it?

I am using ASP.NET 4, EF 4, and VS 2010 SP1.