Sitemap robots.txt problem

I am having a problem when trying to verfy my site in google sitemaps.
I get the following error:

We were unable to access the verification file due to a restriction in
robots.txt

I have looked at my robot.txt and I am not disallowing access to that
file or the root directory. I also have tried deleting my robot.txt and
still no luck.

If anyone knows please advise.