1. I'd strongly encourage you to get your server upgraded to a more modern version of PHP now that you're using a ZC version that supports it.

2. The symptom you've reported is probably a bug, and probably only occurs when you don't have an image set on the attribute and aren't trying to actually upload a new one.
Here's a bandage which I think will work for you:
/admin/includes/classes/upload.php
change line 58 from:
Code:
'tmp_name' => (isset($GLOBALS[$this->file]) ? $GLOBALS[$this->file] : ''));
to:
Code:
'tmp_name' => (isset($GLOBALS[$this->file]) && is_string($GLOBALS[$this->file]) ? $GLOBALS[$this->file] : ''));
And then test by updating those attributes, preferably one with... and one without ... an attribute image ;)