I am an Account Administrator, yet am unable to delete projects. I have even looked in Manage Project but cannot see any option to do this. Why?
By design, you cannot manually delete this yourself - even if you are an Administrator or Reseller. The PLUS! Network will automatically delete any project that does not have Players or Media associated to it after 30 days.
The feature exists because often enough you will need to decommission a unit and/or re-commission the same or another unit, and be able restore content to it, at a later date - e.g. if a player is fault and needs replacing. In which case the project remains on the PLUS! Network for this period of time, thus giving you the opportunity to retrieve content easily.