This is a quick fix for a bug introduced in a previous version because I tried to make it compatible with php4 date().
This bug may have made your sitemap invalid because the lastmod date contained the timezone between the date and time.
This version also brings a new feature that could be useful for larger sites.
I noticed that on a site with over 20000 links it may take a lot of time to generate the sitemap index and sitemap files and will put some significant load on the server if google, yahoo or ask will try to access the sitemap every few minutes or hours ( depending on your site's posting/pinging frequency ), so I thought it would be nice to have some kind of cache.
The module will save generated sitemap index and sitemaps in pligg's cache directory ( this means it needs to be writable by the user running the webserver ) and if the cache has not expired yet the module will serve the sitemaps from the cache instead of trying to regenerate every time.
You can set the expire time ( TTL ) and the module will regenerate the sitemap if TTL seconds have passed since the last time it was modified.
You don't need to set any cron job to generate the sitemap files. It will only generate the sitemap if someone/something(google,yahoo,ask) tries to access it.
Another modification related to the caching system is that the site will only ping services if the cache has expired so make sure you set your cache's TTL accordingly.
To upgrade to this version just download and unzip in your module's directory and then to pligg admin -> module management , disable and uninstall the module and then reinstall it so that you can see the new options ( "Use Cache" and "Cache TTL")