Okay, what’s the trick? My co-worker is stuck on an older Mac for now.
Even saving as Photoshop 2.0 on my OS X machine, he can’t open the files. I think he’s got Photoshop 5.5 for OS 9. It doesn’t seem backwards compatible and we really need to share our workload sometimes.
What are you tryijng to preserve in the original image?
Try saving as a TIFF with all of the layer information and no compression. He should be able to open it, and image integrity will be maintained.
We need to preserve the different layers.
He can open the files if they are saved as JPG, TIFF, GIF etc. But we can’t share work unless we can continue working iwht the different layers.
What version of Photoshop are you saving from?
In CS2 or CS3 select “save as” in your file menu,
Select to save as a TIFF
If you look where you selected “TIFF” …ok… look just below that
You should see a series of radio buttons with selectable options like [As a Copy] [Layers] and [Embed Color Profiles]
Select the “Layers” box and you should be good to go.
You don’t need to have a PSD file to retain layering info, as has been stated. I’m not sure when adjustment layers and that sort of thing were introduced to Photoshop, but is it possible you may have more than just image data on the layers that would preclude it from being completely backwards compatible? Is it possible your bit depth is too high? Once again, I don’t know when the various bit depths were introduced in Photoshop, but I know CS3 supports 32-bit depth and the older ones don’t. (Not that I see any reason you’d be editing at that bit depth). I believe 16-bit depth was introduced in Photoshop 5, so that probably isn’t a problem.
I’m just trying to think if there are any other major incompatibilities…
Yup. Did all of that. It’s not maintaining layers. When he opens the file, they’ve been merged, but at least those ones he can open.
We’ve experimentted using really basic images, different post-script levels, and document modes (including 8-bits/channel). No dice.
ETA: We also tried turning off icons and thumbnails (in case there was some OS X proprietary thing happening), we’ve rasterized all text to be sure it’s not a font issue or experimented with layers that only contained blocks of solid colors. We’ve treid to reduce files to the most basic of basics to see if we can find where teh incompatibility is happening, but we’ve been unsucccessful. It seems as if there is some kind of “OS X-only” data embedded in the file somewhere.
The primary error we get is that the “file is not a valid Photoshop document”.
Check whether the Filetype/Application Ressource Tags are set correctly under OSX
Wow. Split platform legacy goodness!
It’s a pain in the but you may have to save the layers as individual lossless files and reassemble the layers on the co-workers mac.
I’m guessing the problem you have is that transparencies aren’t preserved once the image is opened on his mac since it’s flattening images. Very interesting.
Another idea (this will sound weird) is to turn “Maximum Compatability” OFF not ON. This makes adjustments to allow the file to also be compatible with non-Adobe applications and may include additional detritus that earlier versions of PS don’t like.
Other than that… I’m drawing a blank. Sorry.
DING! DING! DING! We have a winner!
How seriously weird is that? Thanks so much, this will make life a lot easier. 
I think there is something glitchy with the OS 9 machine. It has it’s quirks.
Glad to help!