If you have tried to edit the signature file on a Mac only to find that you get an error message when you try to save the changes, your system may have permissions set that conflict with this activity.
To fix this, open the Finder
1. Navigate to ..\Users\Shared\GreetingCardDesignerV4
2. Right click on the folder GreetingCardDesignerV4 and select Get Info
3. At the bottom on the dialogue box, expand the area Sharing & Permissions
4. In the bottom right corner, unlock the dialogue by clicking on the little lock icon.
5. Change the "Privilege" for each entry to "Read & Write"
6. Click the lock icon again to lock your changes
7. Close the dialogue box.
8. Now right click on the file Signature.psd within that folder
9. Repeat steps 2 - 7 for the file to ensure that the permissions of the folder are passed to the file.
10. In Photoshop open the file, make your changes and save the file.