How the reserved slots work
All our game servers offer 2 player slots more than you normally see in the Steam server browser. For example, if the server browser shows 26 slots, there are 28 actual player slots. Those slots are hidden in the server browser and only people that have a special flag set on their account can connect to them.
So when the server appears to be full, you will get an error message if you try to connect through the server browser. To circumvent this you have to connect through the ingame console of TF2.
The server is only really full when the browser shows 28/26 players. In this case nobody can connect anymore. You'll have to wait till it goes back to 27/26 if you have a reserved slot or to 25/26 if you don't.

How to connect to your reserved slot

First you will need to enable your console if you haven't done so yet. You can do this at 'options', 'keyboard', 'advanced', 'enable developer console'

Now look up the IP address of the server you want to connect to, and copy this by selecting the IP and clicking on it with your right mouse button and select 'copy'.

Now open up your console with the ` key, its at the left of your '1' key on USA layout keyboards (standard) and type; connect server ip here