CURL intermittant problem

I have been having problems with a curl script which works normally with 
many different URLs but had a particular intermittant problem with a url 
in the following format:
http://10.20.30.40/00000001/032/023112/filename.phtml?param1=paramvalue1&param2=paramvalue2 
etc etc.

The unusual thing about this URL is that is starts with an IP address.  
I got a lot of failures to connect, so tried a different way to connect 
as all I need is the page as a string:

According to php.net, the function 'file_get_contents()' should work if 
allow_url_fopen is set to TRUE for the PHP installation.  
'allow_url_fopen' is set to 1 in my php.ini file.

http://php.net/file_get_contents
http://php.net/allow_url_fopen

However, 'file_get_contents' also fails to connect to this particular 
URL.  It gives:

"failed to open stream: Connection timed out in 
*/home/shortsta/public_html/live48_test.php* on line *75*

*Warning*: feof(): supplied argument is not a valid stream resource in 
*/home/mysite/public_html/testpage.php* on line *79*"

The target URL works perfectly and quicly if put directly into the 
browser URL line.

Do you know of any other reasons for problems with such a connection?

John