Why am I unable to repurchase the same stock in NRML/MTF if I have sold it in CNC on the same day?

When you sell shares in CNC from your holdings, it creates a sell position for the day. Exchanges net all positions at day-end, so buying the same stock in NRML/MTF would cancel out your positions, creating settlement and margin complications. As a result, you cannot buy the same stock using leverage (NRML/MTF) on the same day you've sold it from holdings (CNC)