I have managed to split the sitemap-extended into two files (sitemap1 and sitemap2), one for album/images and one for news/pages. The album/images are still taking too long to create, so now I will try and split the albums and images... though a little more difficult as you have them in one combined function.
OK now I have the albums separated, and so I have sitemap1 for albums, sitemap2 for news and pages and sitemap3 for images, however the images one is still timing out, I need to find a way to split this... any ideas?
First, update to the just released 1.4.0.1 version. There are some fixes to the sitemap in there, regarding validation. (the sitemap.php file is not used anymore).
About your error this might be an exif issue or or just too many images. How many images do you have on that site? Do you have the google extension enabled? If try what happens if you disable that.
For slitted sitemaps by type we would have to add/use separate calls like `?sitemap-new` or `?sitemap-images`. That should be possible. For suggestions like this please use the ticket system.