If you get this error, that means have forgot to register a clientfield on either the gsc side or csc, you can check which is missing by adding the following dvar in the launcher.

+set com_clientfieldsdebug 1

Then you launch the game again, and open the console with

Shift + ~

Scroll up till you see “Clientfield mismatches”,  example below of how it could look like.

Clientfield mismatches :

CSC 'toplayer' set does not contain field 'clientfield_gsc_side'
GSC 'toplayer' set does not contain field 'clientfield_csc_side'

Explanation:

CSC 'toplayer' set does not contain field 'clientfield_gsc_side'

• This means you have forgotten to register the clientfield on the client side.

GSC 'toplayer' set does not contain field 'clientfield_csc_side'

• This means you have forgotten to register the clientfield on the server side.