Working with a few files this morning, all of a sudden one won’t save, the rest are fine. I kept getting an error message when trying to save, screenshot attached. Funny thing is that I was able to save my work out as a V5 file, but V6 wouldn’t save it at all 
I’ve added a reference to this thread to the bug report for this problem.
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Hi, Milezee,
We have received several reports of the behavior you describe, but have not been able to repeat it. We have lots of speculation as to possible causes (virus/malware checking software, operating system changes to write permission processes, and so on, but we have no facts).
From your report, it appears that the problem you are seeing is intermittent. Did Rhino resume saving again at some point?
It may help use if we can get a complete account of low-level error messages that are generated when such a failure occurs. If you find yourself in this situation again and can repeat the failed saving situation, please consider using these instructions
to install a Microsoft tool called dggview.exe and sending us the error log.
Thank you for reporting the problem and for any additional light you might be able to shed on what is causing this problem.
– Dale Lear
hi Dale, I had about 5 files open, and it was just one of them that wouldn’t save and this error message came up. I shut down Rhino after managing to salvage the file as a V5 format, then restarted and it seemed fine. I will try the windows debug when back in the office, cheers 
Hi, Milezee,
Thank you for the additional information. Just to be sure I understand, you had about 5 instances of Rhino running and they were viewing different files. Is that correct?
– Dale Lear
yes thats correct, all different models, did a bunch of work on one, did a save and then the error message popped up. I was able to save the others with no problem.