There are two causes for this issue:
- User does not have full access to the object.
- If it is not a permission issue, it may be a character limit issue. The HTML Body field on the Conga Email Staging object is a SFDC rich text field that has a character limit of 32,000 characters. Take a look at the size of the email template body.
WHAT TO DO
Verify that the user has access to the Conga Email Templates object as well as all fields on this object.