Ohiosweetheart,
vBSEO Sitemap Generator uses built-in PHP mail() function, possibly your host doesn't allow that.
Dave-Initial,
check that your host supports mod_rewrite.
Froggy32701,
try to disable text sitemap, remove all files from data folder and regenerate sitemap.
TheInsaneManiac,
do you have sitemap files (sitemap_index(1,2,..).xml.gz) created in data/ folder?