Tasks sync error when Outlook user sends email with task to EWS user

[Bill Bryson]

I'm using Entourage Web Services. Whenever an Outlook user assigns me a
task, I get an email message in my inbox but I cannot "accept" the task in
Entourage (as I could a meeting invite).

That is bad enough, but I get a yellow shield in the lower right and when I
open the Error window I see a long list of sync errors (tries every 1-2
minutes) with an error of

Could not synchronize record sync: Task Request: <Title>
The error is -19717

I must accept the task using Outlook in order to stop the sync errors.

Can someone record this error number of the error web page?

Thanks, Bill