The advanced sitemaps feature was one that allowed you to generate your sitemap and then edit it online. This feature was a beta prototype which we discontinued some time ago.
We embarked on a revamp of our website and spidering engine some time ago and maintaining the advanced editor along side the new code became inefficient. We took the decision to focus on our key services and get them right.
We are about to introduce more advanced settings and saving of sitemaps again and will be adding new editing features shortly.
Sorry if this caused you inconvenience, however we believe it is for the long term good of the service.