I do realise that it's commented out by default, but for those that choose to uncomment it, it will cause an error when validating the page.
Fix:

Open: styles/prosilver/forumlist_body.html
Find:

<img src="{T_THEME_PATH}/images/feed.gif" title="{L_FEED} - {forumrow.FORUM_NAME}" />

Replace With:

<img src="{T_THEME_PATH}/images/feed.gif" title="{L_FEED} - {forumrow.FORUM_NAME}" alt="{L_FEED} - {forumrow.FORUM_NAME}" />