Adapted from Adobe TechNote 329996
When you try to open an image in Adobe Photoshop by double-clicking it or dragging it to the Photoshop icon in the Dock, Photoshop starts, but the image doesn't open.
You can open the image in Photoshop by choosing File > Open.
You installed Photoshop and then used the Archive And Install method to upgrade to either Panther (Mac OS X v10.3) or Tiger (Mac OS X v10.4).
When you start Photoshop, it displays the error message, "One or more files in the Adobe Application Support folder, necessary for running Photoshop, are missing. Please run the Photoshop installer and re-install Photoshop."
Do one of the following solutions:
Solution 1: Copy the Adobe Unit Types file to Library/ScriptingAdditions.
Copy the Adobe Unit Types file in the Previous System folder to [hard disk]/Library/ScriptingAdditions.
You can download the file from here. (File is only 4KB).
Solution 2: Create a new ScriptingAdditions folder, and then reinstall Photoshop.
1. Create a new folder in [hard disk]/Library and name it ScriptingAdditions.
2. Remove and reinstall Photoshop.
Solution 3: Make sure there is no space in the ScriptingAdditions folder name.
If you use the Archive and Install method to upgrade to Panther or Tiger or Leopard after installing Photoshop in a previous version of Mac OS X, the system doesn't copy the Adobe Unit Types file to the ScriptingAdditions folder. Reinstalling Photoshop restores the Adobe Unit Types file, which enables you to open files in Photoshop by dragging them to the Photoshop icon in the Dock.
NOTE: Also Photoshop Elements needs this same file for the very same reasons.