I have a temporary solution that worked for me. Find your file includes\init_includes\overrides\init_templates.php. On that file find the following code on line 41:
PHP Code:
$template_dir = 'classic';
if(isset($_GET['template_switch_id'])){
zen_setcookie("zctemplate", $_GET['template_switch_id'], time()+(60*60*24*365));
$template_dir = $_GET['template_switch_id'];
} else {
if(isset($_COOKIE["zctemplate"])){
$template_dir = $_COOKIE["zctemplate"];
zen_setcookie("zctemplate", $_COOKIE["zctemplate"], time()+(60*60*24*365));
}
}
and change it to:
PHP Code:
$template_dir = 'classic';
if(isset($_GET['template_switch_id'])){
zen_setcookie("zctemplate", $_GET['template_switch_id'], time()+(60*60*24*365));
$template_dir = $_GET['template_switch_id'];
}
the only problem with this solution is that the chosen template will not be stored in a cookie for future visits.
I have this addon installed in one of my websites and works fine. I installed the same files on a different website and ran into the same problem you did.
If I find a better solution I'll post it here.