[kh99]

The reason you're having a problem is because if you look at where that phrase is used in the FORUMHOME template, it looks like this:

<h3 class="blocksubhead"><img src="{vb:stylevar imgdir_misc}/users_online.png" alt="{vb:rawphrase currently_active_users}" />{vb:rawphrase currently_active_users}</h3>

so you can see that it's used both as the text you see and as the 'alt' attribute, so you cannot include html in that phrase. What you would need to do is put your <span> tag in FORUMHOME instead of in the phrase.