Esto es lo que me aparece
24/058/2017 21:58:54 - INFO - <- This level is successfully initialized
24/058/2017 21:58:55 - INFO - Flashtool Version 0.9.23.1 built on 11-01-2017 15:12:00
24/058/2017 21:58:55 - INFO - Executing search strategies to find proxy selector
24/058/2017 21:58:55 - INFO - No proxy found for IE. Trying next one
24/058/2017 21:58:55 - INFO - Strategy firefox failed trying next one : No Firefox installation found
24/058/2017 21:58:55 - INFO - No proxy found for java. Trying next one
24/058/2017 21:58:55 - INFO - Syncing devices from github
24/058/2017 21:58:55 - INFO - Opening devices repository.
24/058/2017 21:58:55 - INFO - Scanning devices folder for changes.
24/059/2017 21:59:00 - INFO - Pulling changes from github.
24/059/2017 21:59:01 - INFO - Quietly closing devices repository.
24/059/2017 21:59:01 - INFO - Devices sync finished.
24/059/2017 21:59:01 - INFO - Loading devices database
24/059/2017 21:59:01 - INFO - Loaded 94 devices
24/059/2017 21:59:01 - INFO - Starting phone detection
24/059/2017 21:59:05 - INFO - Device disconnected
24/059/2017 21:59:12 - INFO - Device connected with USB debugging off
24/059/2017 21:59:12 - INFO - For 2011 devices line, be sure you are not in MTP mode
24/059/2017 21:59:15 - INFO - Device connected with USB debugging on
24/059/2017 21:59:16 - INFO - Connected device : Sony Xperia Z3
24/059/2017 21:59:16 - INFO - Installed version of busybox : N/A
24/059/2017 21:59:16 - INFO - Android version : 6.0.1 / kernel version : / Platform : 32bits / Build number : 23.5.A.1.291
24/059/2017 21:59:16 - INFO - Phone in recovery mode
24/059/2017 21:59:16 - INFO - Root Access Allowed
24/059/2017 21:59:18 - INFO - Device connected with USB debugging on
24/059/2017 21:59:22 - INFO - Connected device : Sony Xperia Z3
24/059/2017 21:59:22 - INFO - Installed version of busybox : N/A
24/059/2017 21:59:22 - INFO - Android version : 6.0.1 / kernel version : 3.4.0-perf-gc14c2d5 / Platform : 32bits / Build number : 23.5.A.1.291
24/059/2017 21:59:22 - INFO - Root access denied
24/059/2017 21:59:44 - INFO - Selected Bundle for Sony Xperia Z3(D6603). FW release : 23.5.A.0.575. Customization : Kernel Only
24/059/2017 21:59:44 - INFO - Preparing files for flashing
24/059/2017 21:59:44 - INFO - Please connect your device into flashmode.
24/059/2017 21:59:58 - INFO - Device disconnected
24/000/2017 22:00:37 - INFO - Opening device for R/W
24/000/2017 22:00:37 - INFO - Start Flashing
24/000/2017 22:00:37 - INFO - Processing loader.sin
24/000/2017 22:00:37 - INFO - Checking header
24/000/2017 22:00:37 - ERROR - Processing of loader.sin finished with errors.
24/000/2017 22:00:37 - INFO - Ending flash session
24/000/2017 22:00:37 - ERROR - null
24/000/2017 22:00:37 - ERROR - Error flashing. Aborted
24/000/2017 22:00:38 - INFO - Device connected in flash mode
24/000/2017 22:00:47 - INFO - Device disconnected