Client issues

Sliding / ice skating when moving and/or a flashing network icon is displayed

The framerate is too high (your PC is too fast). You can set the cl_showfps cvar to 1 (or 2, if you use SoFplus) to display the framerate (e.g. set cl_showfps 2). Workarounds:

In a mutliplayer game, the cl_maxfps cvar can be used to set the maximum framerate (e.g. set cl_maxfps 60). This does not work in a singleplayer game.
In a singleplayer game, the _sp_cl_frame_delay cvar can be used to set a delay in ms between frames (e.g. set _sp_cl_frame_delay 16). This also works in a multiplayer game, but cl_maxfps is better then.
The gl_displayrefresh cvar can be set to display refreshrate. Setting it to 60 (Hz) usually works (e.g. set gl_displayrefresh 60). If it is set to an unsupported value, the game may be unable to switch to fullscreen mode.
Vertical sync (vsync) can be forced on in the drivers of your video card. You may also have to disable variable refresh rate (VRR) technologies like G-Sync, FreeSync, Adaptive-Sync, Enhanced Sync or Fast Sync.

Fullscreen mode not working

This can have multiple causes:

The selected video mode resolution is not supported by your monitor and/or videocard. Choose a different video mode.
The gl_displayrefresh cvar is set to an unsupported value. Setting it to 60 (Hz) usually works, but it's better to set it to 0, which always works.

SoF fails to start (crashes immediately). Windows displays an appcrash report for SoF.exe.

This can have multiple causes:

The video drivers may return a GL_EXTENTIONS string that's too long. Install SoFplus client or the fixed ref_gl.dll. Both can be found elsewhere on this site.
The user directory may not exist or may not be writable by the current user. See the Windows 7 page for more information.

An error message is displayed when connecting to a server: CONNECTION REFUSED! VERBINDUNG VERWEIGERT! CONNEXION REFUSEE ! Incorrect password Ungültiges Passwort Mot de passe erroné Incorrect spectator password Ungültiges Zuschauer-Passwort Mot de passe spectateur erroné

A lot of servers are password protected, because renting a server is cheaper that way. Most password protected servers use 'player' as the password and 'specme' as the spectator password.

The multiplayer server list does not show any servers

This can have multiple causes:

Your firewall may be blocking network traffic.
Your SoF is querying the GameSpy master server at master.gamespy.com, which has been shutdown on 2014-05-31. Use an alternative master server.

Server issues

The server shows weird steam / has weird gun sounds (e.g. on the dm/nycctf1 and jpn3 maps): This may be related to the SoFplus server _sp_sv_weapon_* cvars. Set all those cvars to -1 and the problem may go away.
The server crashes after executing a .cfg file: The .cfg file may be too big. The console buffer size is 8 kB. Split the file up, or convert it to a .func file.
The server crashes for unknown reasons: SoFplus server does not support bots. Remove the bots and the problem may go away.
The server feels laggy (guns fire long after pressing the fire button): The current map may have been running for too long. Change maps at least once a day. If this doesn't fix the problem, the server may have been running for too long and an internal counter may have overrun. Restart the server at least once every three weeks.
Clients timeout when changing maps: Don't set _sp_sv_maxclients_per_ip too low (use 0, or some value above 8).