Hearts have rejected an offer from Rangers to renegotiate terms of payment for Lee Wallace and David Templeton.
The Tynecastle club are owed £800,000 in fees following the transfers of the left-back and winger.
With Hearts under the threat of a winding-up order over a tax bill of almost £450,000, Rangers said they would hand over £500,000 now.
But Rangers wanted to close the deals with that gesture and Hearts owner Vladimir Romanov has dismissed it.
Scotland defender Wallace moved to Ibrox in a £1.5m deal in July 2011, with instalments unpaid when Rangers were destined for liquidation.
Agreeing to pay football debts was part of the agreement that allowed the Charles Green-led consortium to acquire Scottish Football Association membership when they relaunched Rangers over the summer.
Rangers had agreed to pay Hearts £300,000 in January and settle the bill in July with a final payment of £500,000.
Hearts director Sergejus Fedotovas has revealed the club face a £2m shortfall this season and is appealing for fans to take up a share offer.
The Edinburgh club have less than a week to raise money to pay the tax bill to stave off a winding-up order from Her Majesty's Revenue and Customs.
Hearts also face a separate £1.75m tax bill but are disputing the demand - which centres on loan deals for Kaunas players - in a tribunal.