And since you have the byte offset in the file you can explicitly print the offending portion of the input with some context thusly:

perl -le 'open(X,shift())or die "$!";seek(X, 12000, 0)or die "$!";read
+ X, $b, 40;print $b, "\n", " " x 19, "^\n"' foo.xml
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Update: Oop, I see by the paths mentioned you're on Wintendo; you'll probably want to adjust the quotes on that or store it into a file and run that (or just get a real shell and/or OS . . . :)