As the club mentioned at the time, it took us over 6 months to negotiate the deal for McKinstry, and both of the clubs were very keen to work things out amicably. It's just a slow process once the lawyers get involved.
I presume that rather than go with a one-time feem we have tried to negotiate some sell-ons for Hastie (at the expense of lowering the initial payment owed), but Rangers are either dragging their heels or not playing ball. Regardless of the reason, the authorities have more power than HMRC to make them pay up either our agreed fee or one they calculate, as they simply cancel his registration until the cash is coughed up.