Hi Iris
Rel CanonicalThat 26 issues related with rel=canonical not neccasarily an issue like problem it can be recognition like there is a rel=canonical exists. Basicly moz mentions there is that tag involved with that pages.
Duplicate Page Title
Yeah u dont have a duplicated url(as u mentioned it never been created) but u have duplicated page titles related with that page. here is the list of them same title Kenya Luxury.... Pool
http://villasdiani.com/rentals/beach-villas/
http://villasdiani.com/rentals/beach-villas/page/2/
http://villasdiani.com/rentals/beach-villas/page/3/
same problem exists for category/kenya-news/ (4 page)
rentals/beach-villas/ (3page)
rent/family-holiday-home/ (2 page)
category/diani-beach-restaurants-bars/ (2 pages)
To be able to see the mistakes instant and see them all in one place screaming frog is very good tool and up to 500url there is free version available.
/db page have a 404 error
and ur site map is failing for a dns lookup
/sitemap_index.xml
hope that helps
Frutiko Team