WPF binding with viewmodel property

I am trying to bind a commandparameter to a property of the viewmodel class for the view. the project is using MVVM.

<Hyperlink Command="{Binding Path=AddJobAssignmentCommand}">Add Assignment
<Hyperlink.Resources>
<vm:AddJobAssignmentMultiConverter x:Key="AddJobAssignmentMultiConverter"/>
</Hyperlink.Resources>
<Hyperlink.CommandParameter>
<MultiBinding Converter="{StaticResource ResourceKey=AddJobAssignmentMultiConverter}">
<Binding ElementName="lstTechnician" Path="SelectedValue"/>
<Binding ElementName="chkPrimary" Path="IsChecked"/>
<Binding ElementName="dtStartDate" Path="SelectedDate"/>
<Binding Path="StartTime" />
<Binding Path="EndTime" />
</MultiBinding>
</Hyperlink.CommandParameter>
</Hyperlink>

The problem is with the last two parameters "StartTime" and "EndTime". Although both the properties are available in the viewmodel class and in Debug mode I can see that they have value, the parameters are always carrying null value. I have tried binding with a property which is present in the viewmodelbase class, from where this viewmodel is inherited. the parameter gets the value from that property, while I try with any property in the child viewmodel class, it gets null..