This can happen because your software is configured to store documents in ADM and the user processing the remittances has not been set with ADM user details. To check this:
Log into Dimensions as an admin user
Click System, User Records (ribbon menu) or System Control, Users, User Records (classic/module menu)
Select the User Account that is experiencing the issue.
Click Options
Click Set ADM User
Check that the user account registered in the User Name field is correct and enter the password
Select OK. The system should then report that the ADM user account has been validated.
Ask the user to log out and back in and try again.