That may have been an issue in some cases, but even if RH had all the money in hand, they aren't (if I understand correctly) allowed to use their customer's money as collateral. So, RH has to put up their own money as collateral, and it's tied up for two days. They apparently didn't have enough funds to do that, given the trade volume they were experiencing. Also, under normal conditions the collateral requirements would have been a lot less.