Photoshop acting very slowly with one file

[SamMainard]

Hi There,

When I open one 27mb file in photoshop, it suddenly starts acting VERY slowly.

The file has Around 200 layers, but I have used files with more layers then this without problem.

I am using photoshop CS4 on a new macbook pro.

I have attached a few screenshots of my file and photoshop performance preferences.

Cheers.

 

[SamMainard]

Its also worth noting that when I open the file, it takes up about 20 gb of my hard drive space