.NET mediator: Launch exception "Exception has been thrown by the target of an invocation"

Hi,

I am running LoadRunner 12.5.0.0.0 on a .NET 4.5 windows application using the .NET protocol.  When I use the default .NET Recording Filters, the dot_net_mediator launches fine and I can record.  

However, whenever I add our application DLL in the .NET Recording Custom filter and try to record, the dot_net_mediator.exe fails to launch with the following exception:

.NET mediator: Launch exception "Exception has been thrown by the target of an invocation"

What possibly could be the problem? Is there any logs I can look at?

Thank you.