Change:

open(TEMPFILE,">$tempfile") || die "Can't find this temporary file wha
+t is wrong
+. \n";
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to

open(TEMPFILE,">$tempfile") || die "Can't find this temporary file: $!
+\n";
[download]

The $! variable will contain an error message explaining why the open failed. You should almost always include it in error messages about failures of system routines.