CSS Validation bug

Hi,

I get the following message when I try to validate a valid XHTML by file
upload:

File not found: import file://localhost/css/all.css: Operation not permitted


The XHTML file contains inline styling and the following line referencing an
external style sheet:

<link rel="stylesheet" href="css/all.css" type="text/css" />

If I change the relative href to an absolute on the hard disc, the validator
says:

This document validates as CSS level 2.1 !

but at the foot of the page it also says:

No style sheet found

What is one to do or believe?

Regards

Peter Oates