I am suffering from the same errors. I have a server with an eSATA storage system attached to it. While it is network addressed storage it's not like using one of these self-contained no-CPU-having disk boxes which I could see causing problems. I have never had a problem until the most recent version.
The procedure I was using:
I imported a number of books that had the ISBN number in the title field and very little else. Edit metadata - copy/paste number from title to the ID field - click download metadata - click next - select cover and click OK. All looks good. If I click next or OK at the metadata screen I get the error. I click OK on the error and cancel on the metadata screen. Then after a few seconds the title changes to the correct title but nothing else updates. I reopen the edit metadata screen and paste the ID in and download metadata again, click next or OK and error - cancel out. After a few seconds the author changes. About the 3rd or 4th iteration the whole process works.
What concerns me is...even if this is being caused by slow disc access, I clicked CANCEL on the edit metadata screen after it errored yet data is still being modified. Something about that doesn't seem right to me.
Just as a side note - I'd REALLY rather not have to move my 100gb+ library onto non-raided HDD space. Virtually everything I do is on raid-5 disk space or cloud...granted, I do work in I.T. but still...we discourage anyone from storing data locally. I know this may cause a challenge for the developers of this wonderful program but I do hope you can find a way to implement such storage options in the future.