static collection variable not accessible elsewhere

The only way I can think of to reproduce your error is to introduce a naming conflict. Here is a simple analogue:

public class Foo
{
    public String property = 'abcde';
}
public class Bar
{
    public static void doStuff()
    {
        Object foo = 42;
        system.debug(Foo.property);
    }
}

It seems like within your method you must have named some variable opportunities, making it impossible to reference your domain class.