I am also experiencing this very same error. I have tried several suggested fixes from across the internet (including this board). None have been successful. Some of the steps I have tried are logging out and back in, rebooting the system, checking for possible recent Windows or Office updates (none found) and completely removing the Office 365 suite from my system and reinstalling. This error started for me today when I resumed editing a large document I have been working on for a while. The pleasant, natural and understandable default voice that I am so used to using began reading and then suddenly stopped with the error for me to log in. Of course I am logged in and have been the entire time.
Read Aloud is practically unusable. The robotic, harsh voices make it almost unbearable to use. They have horrible diction and the staccato makes it difficult to follow, much less catch the mistakes I am using Read Aloud to catch.
I have submitted a report through the feedback system in word and even referenced this thread in the report. That is something that I would recommend anyone posting this error on here do as well. If they get enough support tickets on it, maybe we can get our pleasant, default female voice back. This is almost unusable this way and even the 'natural' voices you can download suck compared to the default.