Which tool are you using? How does this tie in with Google Sitemaps? <-- the forum section you have posted in
This error occurs in webmaster tools any time I try to fetch then index more than three URLs. The first three always get indexed. After that all I get is the same message that you get. Supposedly, according to Google, I can submit up to 500 pages per month to get indexed. In reality, only 3 can be indexed on any date, limiting the indexing to about 90 pages per month. Never used to be a problem, but since Google keeps fixing WHAT IS NOT BROKEN, more and more things in webmaster tools no longer work the way they should if at all, even on brand new computers.
The only time I get this from Google Fetch is when I'm fetching a page and then submitting at "Crawl this URL and its direct links". It will happen after two times and it's how Google stops you from pounding their system. If you do just one page at a time, you will get the Captcha firing each time. G think you are doing to many in a given time frame. I get this all the time.
I completely agree with mmerlin, the same problem I got all the time when I try to fetch more than two or three URLs. Is there any solution for it? Google Webmasters tools also give the three or four days back report and if we check keyword rank in it then most keywords don't exist as the tool stated in the report.