Invalid feed request error 400

Hi there,
we are very new to creating websites, but so far so good, until now. We are trying to set up feedburner on our site, everything looks good until you click on the feedburner logo, it goes to a page that says “invalid feed request error 400”

Apparently it has to do with a space %20? How do we remove it, and exactly where do we go to remove it?

In steps would be so kindly appreciated…..

Thank you in advance