Validator makes strange things

I was validating my site successfully but when I added /check/referer to 
the link as it is made on other sites 
I got an error, telling me I should correct my !XML! document 
index.php!! Because the "<img>" tag needs a closing tag. But I have one 
" />" Where is the problem that I don't understand?
Thank you for your help in advance,

Received on Monday, 20 January 2003 18:20:54 UTC