NullPointerException while calling Class.newInstance

I am getting a null pointer exception on newInstance line, can't understand why.

There is no constructor in that class.

Also classname_prop is valid, as if it was not valid I would get a classnotfound exception.

 static private MYInterface myInterface = null;
 static{
        try {                   

            myInterface = (MYInterface) Class.forName(classname_prop).newInstance();            

        } 

    }

what can cause this error?