When I try to download a CSV file of a report, I get an error message (ERR_INVALID_RESPONSE).

When I try to download an XML of a survey, I get the following message: "Warning: require_once (PEAR.php) [function.require-once]: failed to open stream: No such file or directory in / var / www / practices .dk / public_html / components / com_cjlib / lib / misc / Serializer.php on line 53 ".

What could be the reason for that?