Hello, have you tried these instructions?
Start by double checking that your firewall is allowing warband access to the internet etc. If that doesn't work try completely disabling your firewall just to make sure.
If that doesn't work try this: My Documents > Mount&Blade Warband > rgl_config
Open up that file and look for these two lines:
use_secure_connection =
max_number_of_connections =
Try changing the use_secure_connection to 0, if it is already 0 change it to 1.
Also, what does it say your number of max connections is? Try changing the number to 5 or 6 instead.
Hope it helps.