Hi,
I'm working in ArcGIS Enterprise 10.8.1.
I have published a feature service with attachments from ArcMap. Attachments can be added in ArcMap.
However I can't add attachments to the feature service - I get this error:

The ArcGIS server error log shows:

I have restarted the service and republished it but it makes no difference.
Does anyone have ideas for fixing this problem?
Thanks
Hanlie