Through the Microsoft newsgroups (thanks Abdulkadar), I was able to resolve this (hopefully permanently) by doing the following.

You'll need to allow a program through Windows Firewall. This can be found in the left hand navigation when you open Firewall. Under the exceptions tab, you'll need to add the following ports:

TCP:

* 990
* 999
* 5678
* 5721
* 26675

UDP:

* 5679

When you add the ports, there will be an option to change scope. You click on that and allow the port for my network only.