Check out error

Hi,

Some of my users are getting this error message when attempting to checkout files 

Error message:
I’m sorry, there was a problem performing the action ‘Download to
‘U:\eB\Test.docx’’, an error occurred during the transfer.
Error: Server Message: ‘<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML
1.0 Strict//EN” “www.w3.org/.../xhtml1-strict.dtd”>
<html xmlns=”www.w3.org/.../xhtml”>
<head>
<meta http-equiv=”Content-Type” content=”text/html;
charset=iso-8859-1”/>
<title>500 – Internal server error.</title>
<style type=”text/css”>
<!--
body{margin:0;font-size:.7em;font-family:Verdana, Arial, Helvetica,
sans-serif;background:#EEEEEE;}
fieldset{padding:0 15px 10px 15px;}
h1{font-size:2.4em;margin:0;color:#FFF;}
h2{font-size:1.7em;margin:0;color:#CC0000;}
h3{font-size:1.2em;margin:10px 0 0 0;color:#000000;}
#header{width:96%;margin:0 0 0 0;padding:6px 2% 6px
2%;font-family:”trebuchet MS”, Verdana, sans-serif;color:#FFF;
Background-color:#555555;}
#content{margin:0 0 0 2%; position:relative;}
.content-container{background:#FFF;width:96%;margin-top:8px;paddin
g:10px;position:relative;}
-->
</style>
</head>
<body>
<div id=”header”><h1>Server Error</h1></div>
<div id=”content”>
<div class=”content-container”><fieldset>
<h2>500 – Internal server error.</h2>
<h3>There is a problem with the resource you are looking for, and it
Cannot be displayed.</h3>
</fieldset></div>
</div>
</body>
</html>

HTTP Error: 500

Seems quite random, looking for suggestions as to how I can debug and fix this?

Thanks.