Pickup assembly through reflection succeeds, Add-Type fails

I am using .net assembly in Powershell. This code works successfully:

[Reflection.Assembly]::LoadFile("E:\Workspaces\RTE\dh.PSP.Common\Mainline\Source\dh.Common.MetaData\bin\dh.Common.Metadata.dll")
$marketMetadataRepository = New-Object dh.Common.Metadata.MarketMetadataRepository

      

        
        
        
      

    

Result:

GAC version location

--- ------- -------- False v4.0.30319
E: \ Workspaces \ RTE \ dh.PSP.Common \ Trunk \ Source \ dh.Common.MetaData \ Bin \ dh.Common .Metadata.dll

So one would think that this would work successfully too:

Add-Type -AssemblyName
"E:\Workspaces\RTE\dh.PSP.Common\Mainline\Source\dh.Common.MetaData\bin\dh.Common.Metadata.dll"

      

        
        
        
      

    

but no:

Add-Type: Could not load file or assembly 'E: \ Workspaces \ RTE \ dh.PSP.Common \ Trunk \ Source \ dh.Common.MetaData \ Bin \ dh.Common.Metadata.dll' or one of its dependencies. The given assembly name or codebase is invalid. (Exception from HRESULT: 0x80131047)

I'm confused as to why one method works and the other doesn't. Any ideas?