It is not possible to generate a valid RSS post address

I have recently set up a blog in Rapidweaver 6. I was successful in getting it posted the first time, although people who signed up for the RSS feed said it was missing the first few sentences of the blog. When I tried to post my second blot posting, I got an error message that said “It was not possible to generate a valid RSS post address from …”. As a result, I was unable to publish my post. I do not know why I got this message, and the only online manual I can find about Rapidweaver RSS feeds is pretty brief in describing how to fill in the various boxes. Why did this happen, and how do I fix it? Any advice on the settings for RSS feeds would be appreciated! Thanks, Stewart