Starting at 01/09/2015 the daily sitemap Generation stoped working. If I try to generate the sitemap manually, the ACP shows working. The Directory for the sitemap contains then only one file (dbseo_sitemap_post_0.xml.gz).
Can you try reducing the amount of items per page in the Sitemap Settings? I'd go for 10000 first and if you still have problems, scale it down to 5000 and try again