Thanks for answering.
I managed to finally save the sitemaps. To do it, I had to give php write access to the home directory. Even then, it still looked as if it went into a loop, and froze Chrome when I left it over night. This time at least the xml and zips are saved.
Let me give you some feedback. Compared to your competitors, your interface is great. The approach of using php to generate the sitemaps are great. The price is great.
However, (as a programmer) there is a few things I would like to give feedback about.
* It is very easy in php to check if the file-permissions is appropriate. You can even write a small file, and then read it back to check if everything is OK.
* I think it is a bad idea to store the xml's directly in the home directory. It is better to store them within the programs directory and then copy them afterwards. This gives a lot less security issues. In my setting, I actually wanted to keep the old (bad) sitemaps in place while going through the process of generating new ones.