Using PHP 5.2 a bug in filemanager.module's function
filemanager_get_area_info() will be triggered: The sizelimit of the current area will be determined by calling the API function
variable_get() with the string
"filemanager_area_limit_" . $area as parameter. Alas the
$area variable at this point is set to the resulting object of the former database query and does not longer contain the area name (usually the name of the calling module like acidfree). Actually this never worked because up to PHP 5.1 the
$area object when used as string just contained the string "Object" (a PHP fallback). So sizelimit was every time looked up for ''filemanager_area_limit_Object'' but never found and set to the default: -1.
Since PHP 5.2 this fallback does not exist and PHP will just throw the error ''Object of class stdClass could not be converted to string'' (see http://us3.php.net/UPDATE_5_2.txt).
The attached patch will fix this.