Are you being served?

One of your customers has an internally written application that manages inbound file transfers from remote locations. After upgrading their computer to Windows 7, the application stops working and remote clients are complaining that their file transfers are rejected before they even start. Which of these is the most likely cause of this issue?

A) The application is licensed only for Windows XP

B) The Windows Firewall is blocking the application

C) The hard drive is out of disk space

D) The end users must also upgrade their operating systems to Windows 7

E) The application has stepped out for an iced coffee