I was having a problem in webmaster tools (also in browsershots) and resolved it with the plugins settings. Just thought id post here to let people know.
I noticed that none of my static pages were in my sitemap, even though the box was checked to include them. Also, my newest categories were being excluded by default. I included all of my categories and made sure the include static pages was checked and rebuilt the sitemap, and it all showed up in my sitemap. one issue resolved.
Also, I was getting the following error in webmaster tools.
URL restricted by robots.txt
We encountered an error while trying to access your Sitemap. Please ensure your Sitemap follows our guidelines and can be accessed at the location you provided and then resubmit.
similarly, when I tried to check my site in browsershots.org, the robots.txt was restricting access there too.
once I unchecked "Add sitemap URL to the virtual robots.txt file" all was well. Webmaster tools was able to read my sitemap and browser shots could find my site.
If anyone is having similar problems, try those settings.
This is still an excellent plugin!
Best of Luck