HELP! possibly lost file twice because of same error... (CS4)

Question

hello.
i have created a poster with embedded smart objects and multiple layers that is fairly complex in photoshop CS4.  I have made this poster twice and each time has taken a day to create the thing. i embedded a smart object that is a floor in the image and using a texture that the client provided.  i had to do it this way because they have not made up their mind about which floor texture they want to use for the poster, and by doing so it would be easier to change the texture if they do change their mind with a smart object.  so, i created a fairly large embedded smart object 'floor' that i had to apply a 'perspective' transform to that layer.  when i did this, the smart object handles go about 4-5 times wider than the actual dimensions of the poster width, which is normal when you apply a perspective transform to an object.  everything worked and looked fine...and i saved everything locally in one folder, including the imported psd 'floor' smart object. 
i have had this major error two times.  i did the exact same process both times i have created this thing and i have gotten the identical error message each time i tried to re-open up this file for changes from the client.  the error is:
"Could not complete your request because the file is not compatible with this version of photoshop"
i really need to open this file without having to recreate it AGAIN.  PLEASE HELP!!!! 
note: when i had the second version of the poster open after i created it again, i did a save as and made a copy because i had to make an A4 size print ad for the same thing, when doing this i converted the 'floor' smart object to a raster layer.  this file does open and i have no problems with it.  but i can not use it for the poster because the dimensions are considerably smaller than the poster and resolution is lost. 
after doing some searching online i have not found any solutions for this and i'm desperate to find anything to get this file open so i don't have to recreate this a third time.  but, if i do not find help i thought i would mention what i believe to be the culprit of the problem...the gigantic embedded smart object with perspective transform that is much wider than the actual dimensions of the document.
any help or advice is GREATLY APPRECIATED!
thanks.

Answer 1

update...
ok. after the third recreation of the file and losing the file again, i downloaded the gimp open up the psd.  this was a suggestion in another forum i read online.  i was able to get the psd open in the gimp.  i then saved a copy with another name and it warned me that i could not save the file because the width of the document was larger than 30,000 pixels.  this was because the smart object perspective 'floor' layer was so wide as i mentioned previously.  i then cropped that layer to the visible pixels on the canvas and saved it as a psd.  then i was able to open the file in photoshop...but i did lose all of my layer styles and all of my masks were moved and had to be redone...but, at least i was not completely starting over so it is better than nothing. 
in conclusion...i suspect the problem is what the gimp said when i tried to save a copy.  don't have your document layers and/or document larger than 30,000 pixels and you should be ok...in case anyone else has run into this problem.