I am not able to sell stocks purchased yesterday

I bought SREI infra stocks yesterday and I want to sell today as it is 4% up.

My sell order has been rejected and when i contacted customer support I have been told that due to Parsi new year I can not sell my this stock today.

Anyone can help to explain as I heard this thing first time.

Today is a settlement holiday, so stocks bought yesterday cannot be sold today. Read this post to know more about settlement holidays and their impact.