One possible problem is that your Network Bridge is preventing you from gaining access. Of course, this is only if you have one installed (I had one to let my box access the internet through a crossover cable).
So here's a super simple way to get rid of the problem (just disabling it won't fix it):
1) Open Network Connections.
2) Right click on the Network Bridge, and select properties.
3) Uncheck all boxes in the upper section. They should say things like Local Area Connection, Local Area Connection 2, etc.
4) Apply the settings by clicking OK/Apply/whatever it says down at the bottom.
5) Go back to the Network Connections window, and make sure it is disabled. If not, disable it.
6) Try again to connect to your box with FlashFXP/your program of choice.
Hope this helps.