error on whos_online page

[211655]

getting this

Warning: mysql_query(): supplied argument is not a valid MySQL-Link resource in D:\vsites\\admin\includes\functions\database.php on line 45
0 -

select session_id, time_entry, time_last_click from whos_online where session_id='a62beacc7b91822b92f93f504b7bdcd5'

 

it happens 90% of the time. some time it doesnt. have on average 100 users