That led me to look at my sanitize sub. What happened was that $file was "sanitized" for character checking. I had a line in sanitize() as follows:

$checks{'data'} =~ tr/\0//d;
[download]

When I commented out that line, the uploadInfo function works.

Sanitizing your data really is a good idea. You can either pull out the Content-Type before you sanitize the filename, or just reject filenames that you don't like:

$filename =~ /^(\w[\w.]*)$/
  or die "Invalid filename\n";
$filename = $1;
[download]

Also, it's strange that your sanitize function would have made a difference at all, unless there were NUL characters in your filenames.