Feedburner error on my blog

Whenever I try to update my “Original Feed” at Feedburner to my new feed URL, I get this error:

The URL does not appear to reference a valid XML file. We encountered the following problem: Error on line 2: The processing instruction target matching “[xX][mM][lL]” is not allowed.

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This is how my header looks like in PHP:
http://pastebin.com/nBEG0mS7

This is how it looks like in HTML:
http://pastebin.com/iMPTdbix

I don’t know what’s causing it. Please help me fix this!