The error code ‘c101b000’ referred to a fault in the market store, failed on downloading progress from microsoft app store. Its solved on my lumia 640. Please try these steps might be solving the error :
- Try connecting to other internet connection or Wi-Fi.
- Check for Windows updates available for your phone.
- Go to Downloads and cancel all the pending downloads.
- Perform a soft reset.
You should have your phone turned on. Press and hold the volume down and Power buttons until your phone vibrates and restarts.
Please note that you shouldn’t touch the device screen during the process not even when the ‘slide down to power off’ prompt appears.