tile server not displaying tiles

I have followed the tutorial for building tile server from packages from switch2osm (very easy to use!)
The problem is, when I go to localhost/osm/slippymap.html, it comes up with a grid of red boxes, the boxes all have a little torn sheet of paper in the top left corner.
If I right click, view images, I get a list of the images it is trying to display:

localhost/osm/17/65707/43723.png
localhost/osm/17/65708/43723.png
.....
But no images are displayed?
If I go to var/lib/mod_tile/default/...
There are a number of directories and subdirectories with .meta files in them (I understand this is the tile data?)

Was wondering if anyone could help in why it is not fully working?