Smartcrawl robots.txt shows 404 page not found

I had a robots.txt file in the site and Smartcrawl showed:

“We’ve detected an existing robots.txt file that we are unable to edit. You will need to remove it before you can enable this feature.”

Then I have deleted this file and check the admin again, now I can see the robots.txt editor. But when I check the robots.txt url it shows 404 page not found error.