I have models released as native FSX models and in fact checking the model file in a hex editor shows that they are native and not port overs but they still cannot show shadows under DX10 but are fine under P3D DX11.

 

For these addons DX toolbox gives the error "Cannot find SMAP Section in Model - Cannot process"

 

What does this mean, and is there anything that can be done to enable shadows in these addons ?

It means that they lack the shadow mapping section in the model which contains the flag to enable shadows.

 

If you google smap and fs developer they have a list of the sections within the model.