Players timeout of server

I have recently come upon something bad to my server, whenever a certain player joins, they timeout once loaded in. It also works for some players, so im not so sure what to do…
This is an error the server is getting:

[ERROR] Virtual clientside lua.:1544: attempt to concatenate local 'str' (a nil
  1. func - Virtual clientside lua.:1544
   2. unknown - lua/includes/extensions/net.lua:32

Im not sure what I should do to fix this. Another thing I should mention is that players are crashing and get returned to the desktop with the error “gmod lua panic not enough memory”.
This is sometimes solved when a player lowers their video settings… Any help is appreciated.