[Pinkie]

I have Windows 8 and the latest version of Calibre. I use a Nexus 7 and a Galaxy Ace to read.
It's all been working beautifully, without a problem. Now, suddenly, I'm getting the "Unable to Communicate with Device" error with both the Nexus 7 and the Galaxy Ace.
I've rebooted, downgraded to an earlier version of Calibre, checked my settings, and to no avail. Here's the error message:

calibre, version 0.9.17
ERROR: Error: Error communicating with device

Failed to create folder: hr=2147500037 facility=0 error_code=16389 description: Unspecified error


Traceback (most recent call last):
File "site-packages\calibre\gui2\device.py", line 85, in run
File "site-packages\calibre\gui2\device.py", line 551, in _upload_books
File "site-packages\calibre\devices\mtp\driver.py", line 400, in upload_books
File "site-packages\calibre\devices\mtp\driver.py", line 376, in ensure_parent
File "site-packages\calibre\devices\mtp\windows\driver.py", line 33, in check_thread
File "site-packages\calibre\devices\mtp\windows\driver.py", line 381, in create_folder
WPDError: Failed to create folder: hr=2147500037 facility=0 error_code=16389 description: Unspecified error

Have no clue what's going wrong. Help!