I have a Nintex account set up as a constant. But I am still getting this error when it tries to move a document into another folder with the same permissions.
Where have you set it? I set the Constant at Farm Level. the account has "Edit" permissions
What action are you using? I am using Copy to SharePoint
Who has started the workflow? A user with "edit" permissions. But in the Copy to SharePoint I use Override Credentials w/ the constant account
I had this same issue, but resolved it by using the Override Credentials and verifying that those creds can change data on the destination library. Before I did this, the action was using the System account to edit the library which did not have access. If you do not provide override credentials, the system account is used.