This is definately a Firewall issue - I bet your member uses Norton Firewall? All the numbers etc look unusual (have you got debug mode on?) but the message itself is what I used to get every time I visited ANY XOOPS site.
Like Mithrandir says, you can do one of two things
1) Inform your user how to set the Firewall to allow redirection of web site addresses. To do this in Norton, Open it, click Options, and the 'Web Content' tab. In there, 'Add' your website, and then, to the right, there are a list of radio buttons to choose from - he will have to set the value 'Remeber Site Redirection' (or something like that) to 'Permit' as opposed to 'dissalow'.
2) That's the long way of doing it and personally, a bit of a nuisance for every member - you'll loose users if they have to do that themselves. Personally, I preferred to just remove the HTTP_REFERRER check totally out of the XOOPS system (a minor secuirty issue but nothing major I don't think - depends on the nature of your site). To disable the HTTP_REFERER check, add the following line at the beginning of the function xoops_refcheck in the file /include/functions.php
return true; // disable HTTP_REFERER check
So, using Dave_L's example, and the way I have done it :
function xoops_refcheck($docheck=1)
{
return true; // disable HTTP_REFERER check
$ref = xoops_getenv('HTTP_REFERER');
if ($docheck == 0) {
...
}
Of course, make a backup copy first and make a note of your change for future upgrades that may overwrite it.
Incidentally, there is a massive posting (20 plus replies) on this subject
here although seeing as you did not know the cause you can be forgiven for not locating it!
Good luck