Hi,
You have all explanations in your screenshot.
Please complete the Address Field - a required custom field
Please complete the City Field - another required custom field
Please complete the Telephone Field - once again, a required custom field
Successfully saved - The configuration is saved
Error while saving the vendor - well, there is an error while saving the vendor, because of the required custom field. So the vendor is not saved, but the configured is.
If you have modified the main vendor in your configuration, there some kind of importance because your modification are not saved.
If you just touch to the HikaMarket configuration, well, it is saved so the vendor not saved is not tragic.
Regards,