Photoshop :: Truncated Files After Save As In 12.1 X64

CS5.5  has worked like a charm until a week ago. All of a sudden pictures I had worked on in PS and saved back to LR3 showed up in LR corrupted. When trying to open them in PS I get the following message: "Could not complete your request because a JPEG marker segment length is too short (the file may be turncated or incomplete)."
 
Oddly, it does not happen to all files I work on, though I am fairly consistent in using the same procedure: I import from my camera to LR (3.6) work on the RAW file in LR and do my fine-tuning of the shot in PS (PS 12.1 x64). In PS I save the file back to LR by using "Save" and add an additional file to an external disk in .jpeg format using "Save as ...".
 
Another odd thing is that there also appears to be a time issue connected to this. After working on my photos, I upload them to my website, and it works fine. After I close PS/LR and reopen again (there could be a reboot in there sometimes), the pictures that were fine previously, are now corrupted. In LR the pic is missing the bottom third (gray snow), split and a color level is missing.
 
If I try to open the picture in Preview, it tells me the file is empty. Quick Look will show the thumbnail, but nothing more. The file in its folder is obviously only the thumbnail as the size is somewhere between 80 - 120 KB.
 
I recently updated my OS to 10.8.2 ...Obviously, this is no way to work. Is there some workaround for this problem, short of having to invest in CS6 and LR4?

Addl info:
Nikon D300, files imported directly from camera without card reader.
I use Topaz and SilverEFEX Pro 2, but it does not appear to have an effect on the truncation
Processor: 2x2.4 GHz Quad-Core Intel Xeon; Memory: 16 GB 1066 Mhz DDR3