Hi Chuck_Mak
Just testing a user that only has Sales level of access to an MYOB Business file I have been able to successfully open invoices from the Invoice page.
If you are experiencing a different situation, I would recommend ensuring that the user doesn't have any other roles assigned to them. You may also want to try to cancel their access and then re-invite them to the file.
If that situation is still occurring then, does the same thing occur if that user logs in on a different computer? Do other users experience this situation or is it just that individual user?