Users Timing Out

[Mossie]

Hey everyone. I started to create my on CS:S SRCDS server and after a lot of google-ing and problem solving, i've finally set it up but there is one more problem which i can not find an answer to.
I got a few of my friends to join my server to test it out, though the problem is, they only get the chance to play for a few seconds and then they lose connection and time out from my server.
I first thought that this might be caused by my router (BT-HomeHub) or possibly my internet connection but i have high hopes that this is not the cause.
Any help will be appreciated, thanks!

[WW2-WARDOG]

Sounds like all the required ports are not open.

UDP 1200 (used for friends service)
UDP 27000 to 27015 inclusive
TCP 27020 to 27050 inclusive
UDP: 27015 and 27020 (default HLDS, SRCDS and HLTV port)
TCP: 27015 (SRCDS Rcon port)