[Xperia Z3v General] BondAR556:
I had issues with flashtool as well. Had the Z3 device driver, flashmode and fastboot drivers installed. Phone was in usb debugging mode and set to allow installation from unknown sources. Still had issues with it saying "Processing of loader.sin finished with errors." .... "Error flashing. Aborted"

I read that someone had success with using an older version of flashtool, so I installed 9.18.4 and tried again.

I got the "Drivers need to be installed for connected device." Reinstalled those three drivers mentioned above and tried again.

Got the loader.sin error again, along with "Cannot identify your device." with a prompt to select a device from the list ( I usually chose Z3 (D6603) up until now).

BUT this time I hit cancel and was told "You can only flash devices."

I unplugged my phone, reloaded the ftf, hit flash and it began flashing!

Hope this helps.

The log below is continuous, I split it up for some clarity

Here's my log (was flashing to .376 before rooting to install prerooted lollipop):

17/052/2015 20:52:51 - INFO - Flashtool Version 0.9.18.4 built on 12-05-2014 22:00:00

17/052/2015 20:52:51 - INFO - Executing search strategies to find proxy selector

17/052/2015 20:52:51 - INFO - No proxy found for IE. Trying next one

17/052/2015 20:52:51 - INFO - Proxy found for firefox

17/052/2015 20:52:51 - INFO - Syncing devices from github

17/052/2015 20:52:51 - INFO - Scanning devices folder for changes.

17/053/2015 20:53:02 - INFO - Pulling changes from github.

17/053/2015 20:53:02 - INFO - Devices sync finished.

17/053/2015 20:53:07 - INFO - Device disconnected

17/053/2015 20:53:57 - INFO - Selected Bundle for Sony Xperia Z3 (D6603). FW release : 23.0.E.0.376. Customization : VER

17/053/2015 20:53:57 - INFO - Preparing files for flashing

17/055/2015 20:55:38 - INFO - Please connect your device into flashmode.

17/055/2015 20:55:58 - INFO - Opening device for R/W

17/055/2015 20:55:59 - ERROR - Drivers need to be installed for connected device.

17/055/2015 20:55:59 - ERROR - You can find them in the drivers folder of Flashtool.

17/055/2015 20:55:59 - INFO - Start Flashing

17/055/2015 20:55:59 - INFO - Processing loader.sin

17/055/2015 20:55:59 - INFO - Checking header

17/055/2015 20:55:59 - ERROR -Processing of loader.sin finished with errors.

17/055/2015 20:55:59 - INFO - Ending flash session

17/055/2015 20:55:59 - ERROR -

17/055/2015 20:55:59 - ERROR - Error flashing. Aborted

17/056/2015 20:56:01 - INFO - Device connected in flash mode

17/057/2015 20:57:04 - INFO - Device disconnected

***2nd attempt (after reinstalling drivers)***

17/001/2015 21:01:34 - INFO - Selected Bundle for Sony Xperia Z3 (D6603). FW release : 23.0.E.0.376. Customization : VER

17/001/2015 21:01:34 - INFO - Preparing files for flashing

17/003/2015 21:03:09 - INFO - Please connect your device into flashmode.

17/005/2015 21:05:21 - INFO - Device connected in flash mode

17/005/2015 21:05:21 - INFO - Opening device for R/W

17/005/2015 21:05:21 - INFO - Start Flashing

17/005/2015 21:05:21 - INFO - Processing loader.sin

17/005/2015 21:05:21 - INFO - Checking header

17/005/2015 21:05:21 - ERROR - Processing of loader.sin finished with errors.

17/005/2015 21:05:21 - INFO - Ending flash session

17/005/2015 21:05:21 - ERROR -

17/005/2015 21:05:21 - ERROR - Error flashing. Aborted

17/005/2015 21:05:22 - INFO - Device connected in flash mode

17/006/2015 21:06:23 - INFO - Device disconnected

17/007/2015 21:07:51 - INFO - Device connected with USB debugging off

17/007/2015 21:07:51 - INFO - For 2011 devices line, be sure you are not in MTP mode

17/007/2015 21:07:52 - INFO - Device connected with USB debugging on

17/007/2015 21:07:52 - ERROR - Cannot identify your device.

17/007/2015 21:07:52 - INFO - Selecting from user input <-- I hit Cancel instead of selecting device

17/008/2015 21:08:07 - ERROR - You can only flash devices.

17/009/2015 21:09:44 - INFO - Device disconnected

***3rd attempt***

17/010/2015 21:10:11 - INFO - Selected Bundle for Sony Xperia Z3 (D6603). FW release : 23.0.E.0.376. Customization : VER

17/010/2015 21:10:11 - INFO - Preparing files for flashing

17/011/2015 21:11:44 - INFO - Please connect your device into flashmode.

17/012/2015 21:12:20 - INFO - Device connected in flash mode

17/012/2015 21:12:20 - INFO - Opening device for R/W

17/012/2015 21:12:20 - INFO - Reading device information

17/012/2015 21:12:20 - INFO - Phone ready for flashmode operations.

...

... (after a bunch of operations)

...

17/018/2015 21:18:12 - ERROR - Error parsing TA file. Skipping

17/018/2015 21:18:12 - INFO - Ending flash session

17/018/2015 21:18:12 - INFO - Flashing finished.

17/018/2015 21:18:12 - INFO - Please unplug and start your phone