I've got the same problem:
Windows 10\Windows 8.1 (on my laptop), GCA b.4.0.423 (with
updates), path to folder: "F:\GURPS Character Assistant 4\", default gds file.
1) Create new character
2) Add to "Language - Native (Spoken)" Advantage
3) Save and then try to open my saved character, but crash with "Runtime error 13: type mismatch"
4) Open gca file in notepad++ and delete everything in [Bonuses] section. Save and open file in GCA - everything is fine!
5) Resyncronize (select default checkboxes), save and open, but crach again with the same error...
This problem appears with all my saved characters, but some of them doesn't crache until i go to the "Tools - Oprions" or try to resynchronize them.
How can i fix this?