Try to update again.  Odd that php reports it can't open the file if it does exist.  Can you do a ls -al. Of that directory
today I received an email report with this
code below.
I have little experience .. I am more and more confident
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Critical Error</title>    
<style>
        body {
            margin: 30px 40px;
            background-color: #f6f6f6;
        }
        .error-container {
            padding: 50px 40px;
            font-family: "Helvetica Neue",Helvetica,Arial,sans-serif;
            font-size: 14px;
        }
        h1 {
            margin: 0;
            font-size: 48px;
            font-weight: 400;
        }
        h2 {
            margin: 0;
            font-size: 26px;
            font-weight: 300;
        }
        a {
            color: #336699;
        }
        p.back-to-home {
            margin-top: 30px;
        }
        p.debug{
            padding: 20px 0;
            font-family: "Courier New", Courier, monospace, serif;
            font-size: 14px;
        }
        .info {
            border: solid 1px #999;
            padding: 5px;
            background-color: #d9edf7;
        }
    </style>
  </head>
  <body>
    <div class="error-container"><h1>Critical Error</h1><p>Could not connect to the database.</p></div>
  </body>
</html>