Redirect loop problem on IIS

I’m having a problem with a wordpress blog on a windows server. Every couple of days the homepage fails to load and firefox gives a redirect loop error, meaning the redirect will never finish. I have a canonical url redirect within the web.config file and I noticed that if I simply download the web.config file and reupload it, the homepage comes back up. Any clues on why this is happening and how it can be fixed?

Thanks so much! Let me know if you need any more info.