Problem with Sitemap plus, cannot export, is there an alternative?

This is a known issue.

The current version is 3.1.0. Install the latest version and you should be OK.

http://yourhead.com/sitemap

Having said that, there might be an issue with Sitemap Plus and the latest RW beta. RapidWeaver 8.2 Public Beta 1 (20697b) — UPDATED BUILD