After the upgrade our users are unable to view some existing attachments or add new ones. We get an error.
I feel like I may have read something in the documentation about this, but I can’t find it now, of course. Anyone have any idea what to do?!
I had a similar issue with attachments when upgrade from 10.2.300 to 10.2.700, in my case the problem was caused by the empty field XFileRef.DocTypeID as shown in your screenshot.
I made this for fixit:
1.-
In Attachment Type Maintenance:
Set storage type to File System
Set Base URI to \\yoursharedstorage\
Set Transfer Type to File Transfer Using Service
Check Enable and Company Default
2.-
Verify that in Document Type Maintenance your Type ID exists.
Eg:
Type ID: CustomerPDF
Description: My Customer PDF
Storage Type: Attachment Link
File Tranfer Mode: Alway Use Company Level Settings
BaseURL: \\yoursharedstorage\CustomerPDF
3.- Fix empty XFileRef.DocTypeID records with DMT or ServiceConnect (I use this one).
4.- Test.
Thank you, @victorcarabez - not sure why I’m just now seeing your reply from a year ago, but thank you. I will follow your steps and test it out tomorrow morning. 
