rebuilding sitemap causes too many http requests to the server

Hi
whenever I try to rebuild the xml sitemap on a website with around 10000 nodes the process aborts with the following error: An AJAX HTTP error occurred. HTTP Result Code: 403 Debugging information follows. Path: /batch?id=1505&op=do StatusText: Forbidden ResponseText: 403 Forbidden 403 Forbidden Access to this resource on the server is denied!
The server is banning me because of too many requests in a short time, it seems that the ajax updating the page with the progress bar is making too many requests. I've tried to play with some parameters to try to make the rebuild quicker but nothing works.
Any help appreciated.
Thanks