Hi, maybe you can look under JoomSEF - Payed. I had the same problem just until now. Maybe my solution works also for you.

Solved.
The solution for me was that Sitemap.xml file could not be made. The location of sitemap.xml (or whatever specified name) is in the root by default. This is mysite/public_html. The root is protected from writing (map attributes). So any new xml can not be written.
What I did is upload my local sitemap.xml to the server. On the server I changed the file attributes of sitemap.xml. Then I went to the Joomla backed, JoomSEF sitemap: pressed Generate XML and it works without problem.

Hi,
I installed JoomSEF succesfully, including the virtuemart extension. All works well with the exception of generating the sitemap. I have marked 'indexed' and saved. When I press Generate XML I get the following error message:

Error Generating XML: Cannot create the specified XML file.

Help is welcome. Thanks in advance.

Joomla version: 1.5.15
JoomSEF: 3.6.1
PHP: 2.11.6