I tried to access your site, but I'm getting a database error message.
I found a bug trying to replicate this, under "My Stuff" there is a "Subscriptions" link which will show your users what subscriptions are available and which they belong to, the bug appears to be with a missing form method within the subscription
s.tpl file, find:
<form action="{ubb url="ubb=subscription&id=`$subs[sub].group`"}">
Replace with:
<form method="post" action="{ubb url="ubb=subscription&id=`$subs[sub].group`"}">
The bug should affect anyone with subscriptions since the HTML5 header was added in 7.5.8; HTML5 doesn't seem to want to allow a missing method to work, and since there is no method I guess it just doesn't send data.
The URL of the information to a specific subscription would be either (example ID is 6):
SE Friendly: ubbthreads.php/ubb/subscription/id/6
Non-Friendly: ubbthreads.php?ubb=subscription&id=6
The subscription
s file is the subscription list, the subscription file is for each "about" page, your link has subscription
s with an ID, where did you get this URL?