在Raspbian上编写Apache HTML

I currently have a PI3 on my home network. With my LAMP apache, I keep the www folder on the USB drive - let's call it /media/USB32/www.
Oh- the USB partition is formatted as FAT32.

Assume my user id is Tony. I have added this user-id to group www-data.

I can access the www folder for editing from a Windows PC, and I can read and write on it using puTTY.

Apache can show a webpage on it, but Apache cannot write or update a file on it via a HTML Form using Fopen or Fwrite.

I'm pretty sure my PHP below is correct.-

function customError($errno, $errstr) {
  echo "<br/><b>Error!:</b> [$errno] $errstr";
        }  
set_error_handler("customError");       //set error handler

echo "HERE GOES OPEN, WRITE and CLOSE";
$fp = fopen('dddata.txt', 'w+');
fwrite($fp, 'Our WRITE data...');
fwrite($fp, 'Some more crap.....');
fclose($fp);

.........

The error given is

fwrite() expects parameter 1 to be resource, boolean given

Any idea where my error(s) are?

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