First thing to try is a hard reset of your router/modem. Make sure family members aren't doing something important on the Internet (critical), then unplug them from power, wait a minute, and plug them back in (assuming you have 2 devices, a router and a modem.. if they are combined, just do the one).  That should reset any corrupted cache info.

If that doesn't work, check firewall software on your computer and any other Anti Virus / Anti Malware software.  See if they are blocking proseries.com and/or our protax20.exe.  

If none of the above works, i'd try a different network just to confirm the problem is yours, if you can.  Tether your phone and use it's wifi to check the link I provided, or if you have a laptop take it Starbucks and use their wifi to check the file (just make sure it's there wifi).