Question about Links in XHTML 1.0 strict

Hi,

I just tried to Validate my Website "http://dreamstate.funpic.de" with 
"http://validator.w3.org" and it worked in the first place.
But after I changed my Website, especially put a "xhtml 1.0 stric" 
button on it with following link:

<a href="http://validator.w3.org/check/referer" target="_blank">xhtml 1.0/en strict</a>

the Validator told me sth like "This page is not Valid XHTML 1.0 Strict" with following error:
>> /Line 106, column 57/: there is no attribute "target".

Why do I get these Error? I looked into the xhtml strict Dtd and on your website, and as far as i understood the target attribute is allowed in xhtml 1.0
strict (i wonder about these error because i used the target attribute on a site that was validated successfully as xhtml 1.0 strict).

Thank you for your help =)

Christoph S.