Try using the .doc instead of .docx. Let me know if this works.
The file attachments are .doc and I'm still receiving the message.
Is this a file upload field? I thought this is a document template.
Are you using Private Cloud or Hosted cloud (Rollbase.com)?
It is an upload field on the record and we are using private cloud.
I was trying to replicate it with the current version 126.96.36.199 but I can't get the error, tried uploading .doc and .docx but seems to be working fine.
What version are you using? also can I have a test XML with that object so I can investigate it.