I got the error message
Warning: implode() [function.implode]: Invalid arguments passed in /home/.garaged/mm/mm.net/blog/wp-includes/post.php on line 1762
by using WordPress 2.8.2 and plugins Google XML Sitemaps v3.1.4, WP Widget Cache v0.25.2, HyperCache v2.3.2 and DB Cache v0.6 together on three blogs with different themes. After deleting all files cached by DB Cache v0.6, disabling the caching process AND deactivation of the plugin the error messages were gone and all blogs came back with better performance.
Maybe we've to wait this plugin will be updated!