After having many live demos go awry, I attempt to avoid live demos as much as possible. That being said, a few thoughts, in no particular order.

I prefer to rely on screenshots and animation which can typically illustrate my product as well, if not better than an actual demo.

Screenshots and animation allow me to craft a narrative that focuses on the products key value proposition.

A live demo often results in an audience member asking a question, then diving deep down into some sort of non-critical feature. A demo based on screenshots with animation will allow you to stay focused on our key narratives and primary value proposition.

If you must give a live demo, you could use a wireless hotspot instead of relying on somebody else's network. Another option would be to run the demo on a remote machine, and show it using a screen sharing tool (such as join.me, WebEx, etc.), so that you're only relying on the firewall to allow HTTP traffic. (Though, that might have a lot of latency.)

Use a screen recorder of video capture software. There are several available at a good price. I agree that you should have a demo in place. But, you can save time by doing a simple demo with a screen recorder. If there is true interest in your app you can then move forward.
Don't stop taking massive action.
Best of Luck,
Michael T. Irvin
michaelirvin.net
My books are available exclusively through Amazon Books. Check out my book "Copywriting Blackbook of Secrets"
Copywriting, Startups, Internet Entrepreneur, Online Marketing, Making Money

My 'simple' answer would be to do record a screencast of your software. There are many advantages to that.

1. No trouble with live screencast, network...
2. You can add some effect (zoom in,..) to focus on specific functionalities
3. You are in control of your time and don't loose your prospect/investor time

I use Screenflow to do my screencast on iOS or OSX. Super user friendly imo.

I hope this helps a bit.

If your prospect/investor wants to see more, this is a good sign, and then you can show more on a 1-to-1 meeting or suggest to install a test version of the app so that they can get their hands on.