5
The error message refers to line "822", but the line displayed is labelled "882". Is that just a typo you made in the post?
Looking at the code in kernel/member.php and kernel/user.php, I would expect $user to have boolean value "false" for this case, so your is_object() check "should" work.
I would follow vaughan's suggestion, but instead of "echo $user;", use "var_dump('user', $user);", which will give you more information.
Bu the way, what's your XOOPS version?