[TYPO3] Problem installing extensions

[Simon Angling]

I've checked fopen is allowed but I am getting this error:

Warning: fopen(/www/vhtdocs/annemcrossan.com/typo3conf/ext/w4x_backup/): 
failed to open stream: Is a directory in 
/usr/local/src/typo3_src-3.8.0/t3lib/class.t3lib_div.php on line 2117

In fact what I did was I put a short test script on the server to test 
fopen - just in case:

<?php
$url = "http://www.google.com";
$fp = fopen($url, "r");
$text = fread($fp, '200');
echo $text;
?>

The script acted as expected so from what I can tell the problem is 
elsewhere.

I have checked the permissions and they all seem OK.

Is there anything else I can check?

Cheers,
Simon