I ran one of those missing link check things. (This one https://www.drlinkcheck.com) and I got three missing 404 errors.
So I downloaded the Latest version of Renita template and two went away but one remained.

404 Not found
http://www.whitchurchwaterway.uk/templates/j51_renita/css/overlays/02.png
Linked from: http://www.whitchurchwaterway.uk/templates/j51_renita/css/vegas.css

The odd thing is that the ones that went and this refer to files in a folder that does not exist. (/css/overlays)

Thought I should report this but I cannot see any effect on the site so its not urgent at all.

Looking at vegas.css lines 17 to 19 read

.vegas-overlay {
opacity: .5;
background: transparent url(overlays/02.png) center center repeat;

There is no 02.png file anywhere in the Template.