How to retrieve list items from session object

I couldn't figure out how to retrieve a list that I stored in a session object, here's what I have:

class EmploymentPeriod with three attributes: ServiceType, BeginDate, EndDate

Dim service1 as new EmploymentPeriod("Gov", BegD1, BegD2)

Dim service2...

Dim lHistory as new List(Of EmploymentPeriod)

lHistory.add(service1)

lHistory.add(service2)...

Session("History") = lHistory

and for debug purpose I placed a gridview to display the periods in the history list so I know there is something in there

Now when I move to a different page I need to retrieve the list

dim lHistory=CType(Session("History"), List(Of EmploymentPeriod))

but I don't get anything

 Any help is appreciated, thanks in advance!
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