Subforms Not Working
Unlike with other database objects, Access does not always use the same 
connection to retrieve the data source of a subform. Access frequently (but not 
always) creates a new connection to SQL Server just to handle the subform 
recordset, or to retrieve the linking field data that connects the subform to the 
main form. Because this new connection does not have the application role 
applied, a permissions error may be generated if you do not have explicit 
permissions to the database object. Unfortunately, this means that there is no 
reliable way to use bound subforms when application roles are applied.The only 
effective workaround is to have completely unbound subforms, with the data 
manipulation handled programmatically. This is the most serious limitation when 
using application roles in Access.