MDbg - Debugger's Protocol Is Incompatible With The Debuggee

I am using MDbg to retrieve a list of all my assemblies listed inside a process' App Domain. Whenever I try to attach a process to the MDbgEngine I receive the following exception message:

The debugger's protocol is incompatible with the debuggee. (Exception from HRESULT: 0x8013134B)

Am I missing something or calling the method incorrectly? I am using .NET Framework 4.0 and the MDbg core reference is taken from \Microsoft SDKs\Windows\v7.0A\Bin\MdbgCore.dll.

Code:

MDbgProcess process;
MDbgEngine mDbgEngine = new MDbgEngine();
process = mDbgEngine.Attach(myProcess.Id); // this line causes the error
foreach (CorAppDomain appDomain in process.AppDomains)
{
   foreach (CorAssembly assembly in appDomain.Assemblies)
   {
      //get assembly information
   }
}

The mdbg locations are at:

C:/Program Files (x86)/Microsoft SDKs/Windows/v7.1/Bin/

for the 3.x version of the Framework and is at:

C:/Program Files (x86)/Microsoft SDKs/Windows/v7.1/Bin/NETFX 4.0 Tools/

for the 4.x version of the Framework. Thank you. Good day.