Hi Bradley2. We have reset the Parallels Desktop 10 for Mac license key. Please follow the below steps to activate your Parallels Desktop 10 for Mac.
1) Open Terminal (Finder --> Applications --> Utilities --> Terminal.app)
2) Execute the command:
prlsrvctl activate-license-online
3) Start Parallels Desktop and try to proceed with the activation once again.
Excellent. all fixed!