Startup/Scratch Disk is full...

[seenew]

I keep getting these errors when I try to crop large photos in Photoshop. This just happened tonight, I mean as far as recent history. I'm running an 800MHz eMac (upgrading to a new iMac in a few months, but this has to work for now), and I've had this problem in the past and solved it by backing up all my files and getting the HD scrubbed.

Is there any other way to fix this? Everytime it has happened before, it's when I am doing something that requires a lot of system resources, such as cropping these 8MP photos. It tells me I should delete some files, but I've got more than ten gigs free on my HD...

PLEASE HELP!

 

[CharlesRobinson]

Your best bet if you're not interested in losing anything is to buy or build an external Firewire or USB2.0 hard drive. You can move some of your files off the disk or simply use it as a scratch when you're working in Photoshop - there's an option that allows you to do this in the Photoshop preferences.

 

[seenew]

I have an external HD, I guess I'll try that.
What exactly IS a scratch disk?
And does this fix the startup disk error that occured at the same time?

 

[seenew]

Okay, I freed up 20GB on my internal HD, and I still get the startup disk is full error.

How can I fix this?