Undefined Index error when uploading files - php

Question

So, I have a form with two input elements: one to upload a file, and the other, a hidden input. Here it is:
<form action="upload.php" method="POST">
upload: <input enctype="multipart/form-data" name="pp" accept="image/png" type="file">
<input type="submit" value="go" />
<input type="hidden" name="eup" />
</form>
on my "upload.php" page (which is a different page), I get the undefined index error. Here's the code for that:
<?php
session_start();
if(isset($_POST["eup"])){
$fERR=false;
if(isset($_FILES["pp"])){ // undefined index error comes if this IF is removed...
$aExts = array("png");
$temp = explode(".", $_FILES["pp"]["name"]);
$tEXT = end($temp);
if ((($_FILES["pp"]["type"]=="image/x-png")
|| ($_FILES["pp"]["type"]=="image/png"))
&& ($_FILES["pp"]["size"]<300000)
&& in_array($tEXT, $aExts)){
if ($_FILES["pp"]["error"]>0){
$ppERR=true;
}
else{
// handle file upload here
}
}
else{
$fERR=true;
}
}
else{
$fERR=true;
}
if($fERR==true){
echo "ERROR";
}else{
echo "GOOD TO GO";
}
}
echo "<br />".ini_get("file_uploads");
?>
I've looked at a bunch of other posts and websites discussing this topic, but none of the solutions worked for me.
by the way, the output of that php is:
ERROR
1

Answer 1

<form action="upload.php" method="POST" enctype="multipart/form-data">
upload: <input name="pp" accept="image/png" type="file">
<input type="submit" value="go" />
<input type="hidden" name="eup" />
</form>