Trying to use SDK as plugin that compiled with .NET Framework 4.0 in Unity

Hello! I am trying to use Canon's ED-SDK in Unity for remote control the camera (It will be our Interactive Photo Booth) to take picture, which is written in C# and compile with .NET framework 4.0. However, Unity and MonoDeveloper is not support .NET framework 4.0 and following Error Message will be showed :

 Unhandled Exception: System.Reflection.ReflectionTypeLoadException: The classes in the module cannot be loaded.
 
 
   at (wrapper managed-to-native) System.Reflection.Assembly:GetTypes (bool)
 
 
   at System.Reflection.Assembly.GetTypes () [0x00000] in <filename unknown>:0 
 
 
   at Mono.CSharp.RootNamespace.ComputeNamespaces (System.Reflection.Assembly assembly, System.Type extensionType) [0x00000] in <filename unknown>:0 
 
 
   at Mono.CSharp.RootNamespace.ComputeNamespace (Mono.CSharp.CompilerContext ctx, System.Type extensionType) [0x00000] in <filename unknown>:0 
 
 
   at Mono.CSharp.GlobalRootNamespace.ComputeNamespaces (Mono.CSharp.CompilerContext ctx) [0x00000] in <filename unknown>:0 
 
 
   at Mono.CSharp.Driver.LoadReferences () [0x00000] in <filename unknown>:0 
 
 
   at Mono.CSharp.Driver.Compile () [0x00000] in <filename unknown>:0 
 
 
   at Mono.CSharp.Driver.Main (System.String[] args) [0x00000] in <filename unknown>:0 
 
 
 Missing method .ctor in assembly C:\Users\Jason\Documents\((MM))\Canon\New Unity Project 5\Assets\Plugins\Canon\EDSDKNode.dll, type System.Runtime.Versioning.TargetFrameworkAttribute
 The class System.Runtime.Versioning.TargetFrameworkAttribute could not be loaded, used in EDSDKNode
 Can't find custom attr constructor image: C:\Users\Jason\Documents\((MM))\Canon\New Unity Project 5\Assets\Plugins\Canon\EDSDKNode.dll mtoken: 0x0a000004
 
 
 

This is a mini project so I have full control of the PC's hardware and software. I think the problem could be solved easily but I just don't know how, I am still too fresh to the IT stuff.