The Maintenance Mode plugin is incompatible with Role Scoper because it forces an early loading of pluggable.php to process the user login and selectively allow front end access during maintenance.
If you can do without this front end access, change maintenance-mode.php as follows:
<!– /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} –>
change
&& !mw_current_user_can_access_on_maintenance()
to
// && !mw_current_user_can_access_on_maintenance()
If front-end access during maintenance is essential, it would be possible to port the required WordPress functions into the plugin rather than calling pluggable.php. However, that would involve some extra plugin maintenance if the WP authentication method changed.