Hey Davor,
I might not have the time to add this patch to the official plugin, but here is a patch that will work.
Open up the pi.catcount.php file and on line number 25 and 26 you should see the following:
$cat_id = $TMPL->fetch_param('cat_id');
$status = $TMPL->fetch_param('status');
Insert the following in between the two lines so it looks like this:
$cat_id = $TMPL->fetch_param('cat_id');
$cat_id = substr($cat_id ,1);
$status = $TMPL->fetch_param('status');
Note that this will only work now if you pass it a url segment that has the C at the front of it.
When I get some more time I will post a solution that can automatically figure out if the C is at the front of the parameter value.
Please let me know if this works for you!
Zac