Message: "Prism cannot start because the serial number file cannot be saved."

Reboot

Really. There is a very high chance this will solve the problem. 

If you use early releases of Prism 6 with Mavericks or Yosemite

Releases of Prism 6.0a, 6.0b and 6.0c will not install properly under Mavericks, or Yosemite and you'll see the message about inability to save the serial number file. Fixed in 6.0d and later.  Update to the latest release using Help..Check for updates. Or write us for help. 

If you used the Mac Migration tool

This problem can occur when you use the Mac migration tool to move Prism  from one computer to another. It is better to do a fresh install of Prism.

After you have run the migration tool, Prism will aks you to enter the serial number. After you enter the serial number and click OK, Prism will pop up a message: "Prism cannot start because the serial number file cannot be saved."

The Prism serial number is stored, in the /Library/Application Support folder, in a hidden file. The Mac migration tool can't  transfer hidden files. The problem is that when the migration assistant tries to transfer the file, it creates a hidden folder of that name instead. The existence of this folder prevents Prism from saving the serial number file. 

This is what you need to do:

1. Set your Mac to show hidden files. 
2. Browse to this folder:          
             /Library/Application Support

1. Find a file or a folder called ssprism5.qxt (for Prism 5) or ssprism6.qxt (for Prism 6). 

2. Delete it.
3. Launch Prism. It will ask for the serial number, and will accept your entry.
4. Reset your Mac to hide hidden files again. 

If these steps don't solve the problem, check out this longer FAQ on what to do when Prism Mac won't launch.