There is no magic XML byte, and XML is text. Here are the things I would do:

• Check the headers that are actually being sent by your server. You could use use wget -S http://yoururl or a Firefox plugin like LiveHeaders

• Check that there is no whitespace before your XML declaration

• Check that your XML is valid with XML::LibXML::Schema - the online validator doesn't check schemas

• Check that your text is UTF-8 print utf8::is_valid($text); print utf8::is_utf8($text)

• Try with plain ASCII data, perhaps with a static file, just to see if that works

If all of the above fails, try posting more of the code, plus a link to the URL that you are sending to OpenSearch, so we can look at it

Clint