stringWithContentsOfURL returns nil

FROM : <archidea
DATE : Tue Feb 05 20:06:07 2008

Hi,
one of my client, only one, gets a null string from the API
stringWithContentsOfURL. His firewall is off.

NSError    *error = nil;
NSString    *aStr = [NSString stringWithContentsOfURL:aURL
                    encoding:NSASCIIStringEncoding error:&error];

The error description is
"File could not be opened." Domain=NSCocoaErrorDomain Code=256
UserInfo={}

How can I detect and fix the trouble?
Should I look into his modem settings? He uses airport extreme.
I have no idea about the solution. Thanks.


Best Regards
--
Lorenzo
email: <email_removed>