Installing for an add-on domain

I have been struggling for 2 weeks to install zen cart for my add-on domain.

I have been trying to install it in a subfolder of my doc root for the add-on. I have no gifs displayed, only red x's.

I then installed zen cart for my main domain and all is well. All gifs display correctly.

This morning I installed it in the doc root, thinking the subfolder was my problem. I still have red x's. The zen cart fles are the only items in my add-on doc root.

Any suggestions?

After reading previous posts, I found htaccess mentioned many times. I went to public_html and renamed .htaccess to .htaccesssav and now my add-on domain gifs are displaying.
(Actually, a new and empty .htaccess file was generated)
This is what was in my .htaccess file:

RewriteEngine on
ErrorDocument 404 /404.shtml

RewriteCond %{HTTP_REFERER} !^http://domain.com/.$ [NC]
RewriteCond %{HTTP_REFERER} !^http://domain.com$ [NC]
RewriteCond %{HTTP_REFERER} !^http://www.domain.com/.$ [NC]
RewriteCond %{HTTP_REFERER} !^http://www.domain.com$ [NC]
RewriteRule .*.(jpg|jpeg|gif|png|bmp)$ - [F,NC]

Is the last line my problem?

Answered elsewhere. Please don't double post.