Application returning Error with possible port communication issue

There's a couple of ways to troubleshoot this.

The first (And possibly easier, especially for the application guys) is to try running fiddler (Or similar) on your client and push all your browser traffic through that. Fiddler will show you were you're connecting what's coming back, content etc. It's good because you see exactly what the browser is sending and receiving.

It may be that you have an issue with content not being re-written for the VS vs the backend IP's/Names

To debug at the LTM, generally the best (Best is relative BTW) way is with tcpdump. You'd need to work out what the correct command line is to just capture the traffic you're interested in. You can then examine using tcpdump (Not really a windows user friendly method) or save the output to a dump file and use something like wireshark to examine it.

There's a long version of this posting (No I haven't written one, but there are lots of answers around - you just have to figure out which one suits you). You'll notice my answer may be a bit vague...

I could also recommend the troubleshooting course from BigIP, it's a great way to learn this stuff.