OK, I assume that you follow all the installation instruction OK..
First: TRY setting TRUE the Use Search-Engine Safe URLs (still in development) in Admin -> Configuration -> My Store
Its probably that you have set TRUE because of your SEF URL contribution
Idea.....
Lets do this..... if it doesnt work you could remove it quickly
1) In catalog/sitemaps.index.php, look the line 99,
its
if ( (SEARCH_ENGINE_FRIENDLY_URLS == 'true') ) {
change to
// if ( (SEARCH_ENGINE_FRIENDLY_URLS == 'true') ) {
if ( (SEO_SITEMAPS == 'true') ) {
2) In your Database add this SQL (phpMyadmin)
insert into configuration (configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, last_modified, date_added, use_function, set_function) values ('Display SEO + Sitemaps', 'SEO_SITEMAPS', 'false', 'Display SEO + Sitemaps.', '1', '999', now(), now(), NULL, 'tep_cfg_select_option(array(\'true\', \'false\'),');
3)In admin -> MyStore ->Display SEO + Sitemaps , set to "true"
4)Try again the sitemaps creation (good luck)
If it doesnt work, you could easily remove the register from the CONFIGURATION table from your database (its only ONE), configuration_key = SEO_SITEMAPS
Regards
Jonatan