D:\Arduino\libraries\SdFat/SdSpi.h: The filename, directory name,
or volume label syntax is incorrect.
The error message above started cropping up shortly after I upgraded to Arduino 1.6.8 on Windows 7 x64. The cause seems to be due to some folder becoming locked in the Arduino compile pathway. One solution seems to be to close the Arduino software, restart it, and attempt to compile again. The program will compile ONCE, and then lock up and fail on a second compile attempt.
This Arduino forum thread recounts the same error: https://forum.arduino.cc/index.php?topic=366757.0
Another workaround seems to be switching the board …