This has happened twice on my server. First time when changing maps after dying and the second time I was playing. The session probably went on for about an hour and a half and the console spit out this error.
Expression Error (ui/error.menu:81): Invalid functionmade it into the stack!
Expression Error (ui/error.menu:56): Invalid functionmade it into the stack!
Expression Error (ui/error.menu:56): Invalid functionmade it into the stack!
Expression Error (ui/error.menu:56): You cannot ! a 'String' (ui_multiplayer)
Expression Error (ui/error.menu:56): Invalid operation - missing parameter inside function or parenthesis
Expression Error (ui/error.menu:56): stray operands in expression
Expression Error (ui/error.menu:61): Invalid functionmade it into the stack!
Expression Error (runtime:0): Invalid functionmade it into the stack!
Expression Error (runtime:0): Invalid functionmade it into the stack!
Expression Error (ui/error.menu:67): Invalid functionmade it into the stack!
Expression Error (ui/error.menu:67): Invalid functionmade it into the stack!
and yes I updated the server.
If this error has already been posted/fixed sorry for the dupe post.