I suspect your problem may be related to how your Slingbox Pro-HD is connecting to your router. I am not personally familiar with your brand of router, but in looking at its manual online, I note that its default is to assign IP addresses dynamically. I found all of my connection problems from outside the home to my SB-PRO-HD disappeared when I programmed my router to assign a static IP address to my Slingbox, and then I programmed my router to forward port 5001 to that static IP address. Page 20 of the online manual for your router describes how to assign a static IP address to devices like the Slingbox, and page 65 describes how to forward a specific port to a specific IP address.
After I did all that for my router, and then power-cycled the router and Slingbox, everything once again worked fine, and has continued to do so.
It seems that you are having some issues trying to set up your Slingbox for Internet Viewing using the Westell A90-9100EM15-10 router.
Even though we do not have the tutorial for this specific model, the following third-party link will provide you with some information that might help you through the settings configuration.
Port Forwarding SlingBox on the Westell A90-750045-07
Just make sure to run the configuration and use the Manual Setup option.