Error when updating or rebuilding sitemap

When I update or rebuild the sitemaps I get the following errors:

warning: XMLWriter::openUri() [xmlwriter.openuri]: Unable to resolve file path in G:\Tom\Sites\drupal\sites\all\modules\xmlsitemap\xmlsitemap.xmlsitemap.inc on line 45.
user error: Could not open file sites/default/files/xmlsitemap/2e9ZfIfLFCC0V-PbcDKUTb1Wk22XgjzJ6f-b16CFlPE/1.xml for writing. in G:\Tom\Sites\drupal\sites\all\modules\xmlsitemap\xmlsitemap.generate.inc on line 158.
The sitemap links were not successfully rebuilt.

When I go back to the previous version rc1, the error is gone.