I/O Error

Dear sir or madam,

i'd like to inform you that i'm getting this error when trying to check
my css:
I/O Error: The host name [www.cplinux.de] couldn't be resolved. Details:
"www.cplinux.de"

The website is online, so it seems to be an error on your validator.
-- 
Mit freundlichen Grüßen / Kind regards
Christian Schramm
<http://www.cplinux.de>