Why does 'scratch file is full' come up on photoshop?

[Stephanie.]

I have just recently got a mac book pro, and have cs5 suite, i just installed it and when i open up photoshop to start a new project it comes up with scratch disk full! I am not quite used to whole mac things yet and was wondering whether anyone could help me with my problem. I'm not quite sure how to change the whole settings of where photoshop should be saving to etc.. all your advice is appreciated, thanks

 

[oldschool006]

I've found that this is a problem when the HD is getting full, restricting CS3 from using a buffer or scratch disc. Clear out some space and you should be fine.

 

[alphaod]

How big are the files you're working worth? How much RAM have you allocated to PS to use?

(Note: Ctrl+K while in PS opens up the preferences)