I am trying to use a model which depends on the Buildings library. The model contains for example

Buildings.Airflow.Multizone.Orifice Orifice1(
            redeclare package Medium = Medium,
            A=0.01,
             m=0.5);

I put the file and a package.mo into a directory which is in OpenModelica's libraries directory, loaded the package, and tried to simulate. I got this error. What is the solution?

"Internal error BackendVariable.getVarAt failed to get the variable at index: 5\nError: Internal error Transformation Module PFPlusExt index Reduction Method Pantelides failed!"