Cannot modify header information – Sitemap error

Got an error when I check on my website sitemap, which errors for a few weeks, today find sometime to try fixing it and it works fine. Note down the fixes done.

Review \WordPress\wp-content\plugins

1. Upgrade wordpress version
2. Check any default wordpress setting to suppress sitemap
3. Update plugins
4. Check any setting in plugin suppress sitemap
5. Update templates
6. Reinstall modules