after 1st trade going against us,if we book loss in CO then another trade is not possible on the same day?even though i have required margin its coming as margin blocked.
Check if any other open orders are there in your order book.
Use the cover order calculator to see exactly how much margin you need.
Check whether that balance is available in your limits area.
If all these are fine, you should not get that error, talk to support team to figure out whats the issue.