A new order I placed got rejected because of insufficient margins, and I noted that the system has blocked additional margins for the existing long option position. Why is this happening?

You might be receiving an alert for insufficient margin rejection for a new order while you hold a long options position due to your existing long position that may have been converted into an ITM option.

All ITM positions should possess sufficient margins in the last week of expiry according to the physical settlement policy.

The Exchange levies physical delivery margins as a percentage of applicable margins of the concerned stock, i.e., VaR +ELM + AdHoc, which is charged from expiry minus 4 days for long ITM options as mentioned below.

Day (BOD - Beginning of Day) Margins Applicable
E-4 Day (Friday BOD)
10% Var + ELM + Adhoc Margins
E-3 Day (Monday BOD)
25% Var + ELM + Adhoc Margins
E-2 Day (Tuesday BOD)
45% Var + ELM + Adhoc Margins
E-1 Day (Wednsesday BOD)
70% Var + ELM + Adhoc Margins

Please note that the margin requirement changes on an intraday basis as well as according to the status of the option (OTM/ITM).