The error is caused by a missing table in the Attaché database, and can be resolved by following the steps below:
In Attache, Select Tools, Company, Track Changes, Track Files. Opening this menu path will perform a quick rebuild of required tables for onboarding.
Close this menu once the mini rebuild has finished (this should only take a few seconds).
Navigate back to your Attaché Online organisation, and go to Employee Onboarding menu.
On the erroring Employee onboarding request(s), click the Actions button, then Review.
Select Resend to your Attache Software.
After a few minutes, the status for the employee onboarding request will change to Completed.
Repeat steps 3 to 6 for each employee onboarding request that was receiving this error.