error when adding products

Hi,

Thank you for the report.

You can fix that by changing the code:
foreach($loadedCategories as $cat){
$categories[$data->product_id][$cat]=$cat;
}

to:
if(!empty($loadedCategories)){
foreach($loadedCategories as $cat){
$categories[$data->product_id][$cat]=$cat;
}
}

in that file.