Why can't I add a Reviewer or Approver to my Test Plan?

 I've created a Project template, with a new Test Plan template and used it to create a new Test Plan in a new project to test the functionality and interactions between DOORS 9 and RPE.  Everything seems to work as expected, except I cannot add a Reviewer or Approver.  It allows me to search and choose the nominated user, but the user is not added to the table (list of reviewers/approvers) below.  I've tried this with multiple Permissions (setting 'Everyone' to do everything) and removing all Pre-conditions and Follow-up Actions.  Am I missing something in the setup of the Project or Test Plan that would stop this?  Incidentally, I can no longer add reviewer or approvers in old projects that I have done this before.  I'm not sure if this is a coincidence or not.  Things to bear in mind are we have recently moved to version 7.0.2 from 6.0.3, so could possibly be a server set up issue or something has changed in the new version that I currently don't fully understand.  This is also just a 'QM' project, i.e. not lifecycle ...etc.  Any help appreciated!!