anyway, i just renewed the _item_comment_form.inc.php file from the skins dir.and its gone (so did my modifications (: ).

This would be hard to fix. It looks like now $PageCache object is not loaded at all in some situations. For that reason you see "Trying to get property of non-object".

We would need to keep loading "PageCache" object to make legacy code in your _item_comment_form.inc.php work in 4.1 Apparently we don't want to do that any more.

I recommend comparing old skin files with their originals in /skins directory after each upgrade. This may not only fix errors, but also allow new features to work in your old skin.