Converter uses its own set of HOOPS libraries. If your application is calling converter.exe in a virtual environment, your application is likely calling HOOPS libraries from other HOOPS toolkits, such as Visualize, instead of from Communicator.
To get around this, in your application that calls converter.exe, explicitly set the environment PATH for the Communicator HOOPS libraries. For example, ProcessStartInfo class has a property called EnvironmentVariables in which this can be done.