Hi Mark,
Please check whether you can attach documents to a new created general journal with this account.
Please check whether the general journal is in a workflow. Usually we can tell from the journal name:

If the general journal is in a workflow and it was submitted, we cannot attach a document.
If the general journal is in a workflow and it is not submitted, we can attach a document.
You can refer to following screenshots:


So documents can be attached for 00471, while cannot be attached for 00459.