Problem: Facebook share button will not show up using WordPress 3.0.1 and Simple Facebook Connect. I tried this with themes Twenty Ten, Twenty Ten Weaver, and an old pre-3.0 default theme based on Kubrick. Your problem may not be with WordPress or the plugin.
First off, this is what I did:
- Set up my Facebook application
- Installed the Simple Facebook Connect plugin
- Activated plugin “Simple Facebook Connect – Base”
- Configured the plugin with the Facebook API key, Facebook Application Secret, and Facebook Application ID I got from setting up the Facebook app
- Activated the plugin “SFC – Like Button”
- Activated the plugin “SFC – Share Button”
The site showed the Facebook Like button but would not show the Facebook Share button. If you viewed the page source, the html xfbml code was present. This really threw me!
Finally, after much unproductive searching on the web, I used the Firefox Firebug add-on to see if I could find out anything. As a part of the page makeup I saw an iframe with an error about a url not being present. Since I had just recently set up the Facebook application, something clicked in my memory. When you are logged in to Facebook to see your application, under “Edit Settings” and then “Website” there are two settings, “Site URL” and “Site Domain”. I had set up the “Site URL” with “http://www.mysite.com/” and I did not have anything entered in the “Site Domain” field.
“Site URL” is your site’s address, simple enough. However, I entered it with the preceding “www” and my WordPress blog lists all my pages as “http://mysite.com” – without the “www” at the beginning. Guessed it yet?
If you look at the help text to the side of the “Site Domain” field, it says, “If set, Facebook will enable authentication on all subdomains (e.g., “example.com” will enable *.example.com)”.
So, I set “Site URL” to “http://mysite.com/” and set “Site Domain” to “mysite.com”.
I refreshed my blog and, voila! The Facebook Share button was now showing.
I realize that Facebook changes the specs and their edit screens for logging in and editing your applications often, but I hope the basic logic of this post is still helpful if you have this problem. Please leave a comment if this helped you out, or if there is anything additional to add. If I’m still set up with a Facebook Like, show me some love. 
