1. Uninstall the vBSEO Sitemap generator. It is old, outdated, and a potential security risk. Mine stopped working on three forums after recent vBulletin 4 updates.
2. Enable the built-in vBulletin sitemap generator as follows:
- AdminCP >> Settings >> Options
- scroll down to XML Sitemap
- Enable Automatic Sitemap Generation = Yes
- Set the remaining settings according to your preferences
- For me, I set Sitemap File Path = . (just a period; you may need to experiemtn a bit with this depending on your server)