& In external URL

I have a web page and i tried it with validator. Most of files are XHTML 1.1 Strict valid. But some (3 or 4 files). The only errors which i have in the files are external links. That are links on other web pages, on files, on which when i click, it starts downloading. And some of that files have & in the name. The probelm is that when if that files are on other servers, i can´t change their names. So with this problem, can my page be XHTML 1.1 Strict valid or no?

Thanks for answer. 
Martin.
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