Photoshop Start Up Disc Full? even though enough space available?

Hi,

I have a white Macbook, bought in 2009 and completely reinstalled it, also all data was removed.

The problem which is currently occurring is whilst I am using PS and try to edit a photo, the message comes up that my start up disc is full!!!

But there are just a couple of songs, a few documents, google chrome, and PS2 on my computer. I didn't even install iPhoto! There is enough space on my laptop.

Here some information:

The right click on the volume says Version 10.6.1, Capacitiy 249.72 GB, Available 158.42 GB, Used 92.3 GB.

Thanks for your help, unfortunately I am not good with computers and hence I am unable to solve the problem which has been already discussed in other boards.