If you are developing to AutoCAD Plant 3D 2014 you may have faced the issue below: ‘Could not load file or assembly PnP3dObjectsMgd (….)’.
A little background information: starting on 2014 release, some vertical products, like Plant 3D, are launched in plain AutoCAD with a startup modifier. This is know as configurable AutoCAD, see more details at this blog post. That way, the AutoCAD folder will have a subfolder /PLNT3D/ with the Plant 3D specific DLL.
But there is a know issue where AutoCAD Plant 3D may not load some required DLLs when a plugin needs it, causing the error message mentioned.
A small trick to solve this exception is ‘help’ Plant 3D find the required DLLs. To do so, create a modify your custom class that implements IExtensionApplication. Inside the Initialize method, include:
Now we can customize how and where the .NET engine will search for assemblies it could not find. We just want to include the /PLNT3D/. That can be done in several ways, here is a example:
object sender, ResolveEventArgs args)
private Assembly TryResolvePlant3D(
string name = GetAssemblyName(args);
string assemblyPath = System.IO.Path.
Combine(PLNT3DFolder, name + ".dll");
Assembly assembly =
if (assembly.FullName == args.Name)
// based on this post
private string GetAssemblyName(ResolveEventArgs args)
if (args.Name.IndexOf(",") > -1)
name = args.Name.Substring(0, args.Name.IndexOf(","));
name = args.Name;
private string PLNT3DFolder