SYMPTOM:
A Strategy User member of the System Administrators Group receives the following warning message when trying to delete a project in Strategy Developer 9.x and 10.x:

'Only the Administrator or the owner can delete the project'
STEPS TO REPRODUCE:
Follow the steps below to reproduce the issue in the Strategy Tutorial project:

CAUSE:
This is working as designed. For security reasons the only Strategy Users able to delete a project are the 'Administrator' user and the owner of the project (the Strategy User used to create the project.)
ACTION:
Use the 'Administrator' Strategy User to delete the project.