Error on View Block validation

Hello!
On my site www.erzone.de i created a Views-Block called "Neueste Events" on the top of the site.
During w3c validation i got following error: Error Line 161, Column 130: Attribute "alt" exists, but can not be used for this element.
…tle="EIS-KALT Über den Wolken " alt="EIS-KALT Über den Wolken ">EIS-KALT Über

The error comes form the first entry oft the block an is caused by the "alt text" .
All other entries in the block make no errrors.
How can i solve the problem?
Thanks!