Once in a while, I will get one of those calls that I have a good feeling that the problem isn’t the network or the firewall. One tool that I have found that is handy to have is a http server that can be fired up at a moments notice. HFS (http://www.rejetto.com/hfs) is a utility that you can run on just about any windows system and doesn’t require anything to be installed. A side benefit is that you can use this to copy files to another machine without using FTP or another option. When I have had to troubleshoot a problem where a web server isn’t responding, I can fire this up and see if the problem is on the subnet, remote machine, etc, you get the idea.
Another option, when troubleshooting a wireless problem is to use the GoodReader app if you have an iPad. It has has a web server function for transferring file to/from GoodReader that is also an option worth trying. Another option worth having in your back pocket is to use the http or https option in a Cisco IOS device as a test point. I would suggest taking a spare device or something like a Cisco 870 that should be had for a just a few dollars. Under no condition would I recommend the use of a production device as a test point unless you had absolutely no other option.