[PeterT]

I just tried downloading the current source (and yes.. I verified that the change you made https://github.com/cbhaley/calibre/c...8b10cc1a37213d was in the driver) and repeated tests while running from source.

Still receive the same error.

Spoiler:

datetime.datetime(2014, 12, 29, 21, 52, 8, tzinfo=tzutc()) is not JSON serializable

Traceback (most recent call last):
  File "site-packages\calibre\gui2\device.py", line 87, in run
  File "site-packages\calibre\gui2\device.py", line 480, in _set_library_information
  File "site-packages\calibre\devices\smart_device_app\driver.py", line 50, in _synchronizer
  File "site-packages\calibre\devices\smart_device_app\driver.py", line 1565, in set_library_info
  File "site-packages\calibre\devices\smart_device_app\driver.py", line 50, in _synchronizer
  File "site-packages\calibre\devices\smart_device_app\driver.py", line 605, in _call_client
  File "site-packages\calibre\devices\smart_device_app\driver.py", line 525, in _json_encode
  File "json\__init__.py", line 243, in dumps
  File "json\encoder.py", line 207, in encode
  File "json\encoder.py", line 270, in iterencode
  File "json\encoder.py", line 184, in default
TypeError: datetime.datetime(2014, 12, 29, 21, 52, 8, tzinfo=tzutc()) is not JSON serializable

I also did verify that the version info displayed was [2.14]*[64bit].