I've have found that my previously working travel form is throwing a workflow approval error ever since I added the Attachments control to the form. If a user submits a form without an attachment it still works perfectly well. However, as soon as a document is attached, the initiator receives an email with subject 'Workflow errored', body: "Error in request approval action. Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))".
Googling this error has led me to check the permissions on the workflow task list - everyone has 'Approve' permissions.
For the list permissions everyone has 'contribute with no delete'.
Any ideas what has caused this? In the workflow request approval I tried changing the item permissions to Approve from Unchanged but this hasn't helped.
It's definitely a permissions issue but I'm not sure what else to change.