Crawl Error

We have re-designed our website & reduced number of pages in new site. In Google webmaster website showing 404 errors. We had tried re-directing old site URL’s to new URL’s. Unfortunately, Business Catalyst (E-Fusion) does not provide the facility to redirect .aspx pages. Then through Google webmaster tool we have requested to remove old URL’s and index new ones. But they blocked my website. Can anyone help me how to remove 404 errors? Is it harmful for my website?