If a setter is unable to view a deal that they are assigned to, first check the customer lead page to verify the setter is actually assigned to the lead, and then the user's settings to check that the office they are assigned to is the same office that is assigned on the lead.
If the user has both setter and sales rep roles, they need to view the lead through the setter dashboard and not the sales rep dashboard. This can be accessed by clicking on My Roles > Setter > My Deals.
All deals that they are assigned to as a setter will show up on this dashboard.