Error synchronising contacts with Google

I am getting the following error message when trying to synchronise my Google contacts with eM Client.

[Google Contacts]Uploading item(s) to folder ‘dave@compton-family.eu/Contacts’ failed due to the following error: Execution of request failed: https://www.google.com/m8/feeds/contacts/default/full (Invalid request.)

This appears to be a long standing problem which, apparently, has been resolved once and now has re-occurred, but I can see no posts saying just how it has been resolved or what I can do to fix the problem.

(PS. Calendar entries are synchronising OK.)