THANK YOU for posting this! I was able to solve the issue thanks to your post. I'll post the fix here for anyone who stumbles upon this post in the future.
 
	Find the following file admin\applications\core\modules_admin\mycp\dashboard.php
 
	Change line 377 to 
 
$online	= $this->DB->buildAndFetch( array( 'select' => 'count(*) as fixme', 'from' => 'sessions', 'where' => "running_time > {$time}" ) );
	Change line 379 to 
 
$stats['active_users']	= $online['fixme'];
	Of course you don't have to use the word "fixme". You can use any word so long as you don't use "rows"!. Thanks!