It really depends on what type of problems the client experiencing. What type of access is causing the problem FTP or HTTP?
It may be that the client's firewall is blocking unrecognized programs from accessing the Next, that could be a problem. As well, make sure they have their proxy settings configured correctly, if applicable.
In short, the client should talk to the network administrator to find out what is going on. Most firewalls keep a log of rejected requests, etc. so that might help track down the problem.
That's more or less what I did (put warnings of possible firewall).
But does anyone now a sertain way of detecting a firewall?
What I have done so far is that I use the action to detect if the computer is connected to the net. If it's not I post a message telling the user that it can eather depend on a firewall or just that he is not connected.
So is there a better way to be sure its a firewall?