error message

Hi there.
I've been using photoshop CS2 for a while now and have recently encountered a problem.
Yesterday after, working on a .PSD file for a week, i tried to open said file and recieved the error message
"This file is not compatible with this version of photoshop."
I've looked up the causes for this and i'm not saving over a network and i don't have norton antivirus installed.
How do i stop this?

Have you gotten any suggestions to solve this? I’m a Mac user and I’m working with CS3 on OSX 10.5.4 and I’m running into the same issue. I have worked on creating 9 files in Photoshop, which are part of a project. I have saved them as PSDs and today when trying to retrieve them I’m getting the following error message with 5 of them: “ Could not complete your request because it is not a valid Photoshop document”. I'm not saving over a network. Please provide some feedback if you have any, I’ve tried everything I can think of to open them and still haven’t been able to…I’m pretty frustrated.