Without knowing what plugins you’re running, the only thing I can say is something is putting 19 bytes of null characters at the start of your feed. That is the reason it won’t validate. (The <?xml…. part has to be the very first characters)
The only option I know of is to start disabling plugins one-by-one to find the offending one.
+1 on this one. I have a blog I support where I’m seeing this.
Did anyone figure this out? I’m getting the exact same error. Same setup – running on IIS. Also, FWIW I’m not using any re-write rules other than the 404 page hack (since my host doesn’t support any real url re-writers)
Granted, it was a bit of a challenge getting the plug-in up and running on IIS, I followed the steps listed here:
http://neosmart.net/blog/2007/getting-wordpress-super-cache-to-run-on-a-windows-iis-or-apache-server/
In addition to the clean-up in wp-cache-config.php shown there in step 8, I had to shorten the path since it duplicated what was already in ABSPATH.
Nonetheless, the option page comes up, but if I try to make any changes on it, this error appears.
