Well that's probably because the argument list is too long ;)
You can write a simple bash loop to get around this; 
for i in $(find . -type f -name "*.xml" -print -exec grep -i '<book></
+book>' {} \;);do grep -i "<name=>*.*Sydney*.*" $i && echo $i;done

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In reply to Re^3: find the xml files by Utilitarian
in thread find the xml files by Anonymous Monk

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