Version missmatch

Make sure you have arena loaded before attempting to join the server, alternatively start quake with the command line option +set fs_game arena.

Set cl_allowDownload to 1 in order to download whatever assets might be missing in your local installation from the server.

Experiencing lag

Try the following in your configuration:

set cl_maxpackets 125
set cl_timeNudge  -12
set rate          25000
set snaps         40

Wrong resolution

Try the following in your configuration. Replace customWidth and customHeight with your resolution of choice:

set r_mode         -1
set r_customWidth  1920
set r_customHeight 1080

Some engines also support set r_mode -2 that will use the desktop resolution

Mouse acceleration

Some windows users are experiencing issue with mouse acceleration even after It’s been turned off. MarkC mouse acceleration fix could solved the issue.