Here's something to try:
While in the Finder and BEFORE launching Photoshop, highlight the icon of the hard drive where the scratch disk resides, do a Get Info (Command I) and see if you can check the box that says "ignore ownership of this volume" or some such verbiage.
I'm not seeing that option in the 'Get Info' screen, however after some Googling it seems like this could work. Is there any way that I can get this option to appear?
EDIT: After a bit more reading, it turns out that the option will not appear if you are currently booted into said harddrive. I'm unsure about how to get around this.
Sorry, I overlooked the fact that you are on a MacBook laptop and are using your boot drive as your scratch disk drive. My bad.
Then, I have no further ideas. 15 GB is way too little space for Photoshop's scratch disk drive, especially when that very small space is being shared with the swap files of the OS. I wouldn't be surprised if the reason only an administrator can run it on your machine is actually a protective measure.
Hm, I'll create and boot into a small partition and try to check the option that way. If that doesn't work, I guess I'll have to do a clean install.
I've used Photoshop when I had even less space than 15GB so I'm unsure about that, but I may clear some stuff out and see if that works anyway.
It's painfully obvious that I'm not qualified to give advice in a situation like yours. Sorry.
Generally speaking, one should NOT partition the only drive in a laptop, as the space available to the swap files of the OS and to the Photoshop scratch disk does not need to be limited a priori by the constraints of partitions.
Of course, I'm deliberately ignoring your apparent need for a Windows partition, because i wouldn't remotely know how to handle that.
I managed to fix this myself, almost by accident, after failing every method suggested that I came across.
My problem was due to 'read only' access being set to some folders in ~/private/ on my main account, meaning that Photoshop could not create an important, temporary scratch file in this location.
To anyone else who comes across this thread due to having the same problem, here's the solution:
- Open finder, then go to 'Go' in the menu bar and select 'Go to folder'
- In the window that opens, enter '/private/' and click 'Go'
- Then, right click on the folder 'tmp' within /private/ and select 'Get info'
- In here, scroll to the permissions section and change the relevent user permissions to 'read and write'
- Before closing this window, click on the gear icon underneath the list of users and select 'Apply to enclosed items' and hit 'Ok' in the next window.
- Finally, repeat steps 3 - 5 for the folder named 'var', also within /private/ and you're done. Photoshop should now open as intended!
Although this solution was ideal for my home laptop, giving 'read and write' access to important folders like these can probably lead to lowered security so please do it at your own risk.
When I do the '/private/' command the OS tells me that the folder can not be found.
The /private folder is a hidden folder. However, if you navigate to Go > Go to Folder and within the Go to Folder window enter just "/private/" without the quotes, then it should take you to the private folder. Make sure you're typing it exactly as it is here. Folder/file names are case sensitive.
Well I tried all of these steps finding the /private/ folder and changing the permissions to 'Read and Write' and the OS is still not saving the changes to the 'ignore ownership' button.