Based on the ContactService.php line it looks like it might be trying to add a contact using the incorrect ID. The other lines referencing BaseService.php line 97 are a bit odd since our normal SDK do not have a line 97 so I'm not sure what it might be referencing.
I would ensure that the code has not been altered, or if it has, that any additional code is correct. Attempt to add new contacts. If you still get the same errors then please reach out to us at firstname.lastname@example.org so we troubleshoot further.