On your pages on the server, the column you are storing in the session is fld_adminID and the session name is SecurityAssist_fld_adminID
YOu should be using the fld_adminACTIVE column in the session.
the fld_adminID column stores the Primary key value, not the grpoup level.
when the user Matthew logs in, the session value is 1 so is not considered a Master Admin.