[Sony Ericsson Xperia Mini, Mini Pro, Xperia Pro, A] ceroberoz:
Its funny because I was found the solution from Arch Community for my previous ia32-libs problem.

There you go, I hope you've found the solution first because I rarely go to XDA unless there is no problem or I am looking for new kernel :p

https://bbs.archlinux.org/viewtopic.php?id=116373

@monjovega, same case here.

Win8 Pro x64 always display this error and of course I am the Administrator of my own PC :D

15/008/2013 01:08:33 - INFO - <- This level is successfully initialized
15/008/2013 01:08:33 - INFO - Flashtool Version 0.9.10.1 built on 2013-01-09 19:49:47
15/008/2013 01:08:33 - INFO - You can drag and drop ftf files here to start flashing them
15/008/2013 01:08:38 - INFO - Device disconnected
15/009/2013 01:09:13 - INFO - Device connected with USB debugging off
15/009/2013 01:09:13 - INFO - For 2011 devices line, be sure you are not in MTP mode
15/009/2013 01:09:20 - INFO - List of connected devices (Device Id) :
15/009/2013 01:09:20 - INFO - - USB\VID_0FCE&PID_E166\BX902NV2B6	Driver installed : true
15/009/2013 01:09:20 - INFO - List of ADB devices :
15/009/2013 01:09:20 - INFO - - none
15/009/2013 01:09:20 - INFO - List of fastboot devices :
15/009/2013 01:09:20 - INFO - - none
15/009/2013 01:09:55 - INFO - Device disconnected
15/011/2013 01:11:42 - ERROR - Drivers need to be installed for connected device.
15/011/2013 01:11:42 - ERROR - You can find them in the drivers folder of Flashtool.
15/012/2013 01:12:14 - INFO - List of connected devices (Device Id) :
15/012/2013 01:12:14 - INFO - - USB\VID_0FCE&PID_0DDE\BX902NV2B6&ZLP	Driver installed : false
15/012/2013 01:12:14 - INFO - List of ADB devices :
15/012/2013 01:12:14 - INFO - - none
15/012/2013 01:12:14 - INFO - List of fastboot devices :
15/012/2013 01:12:14 - INFO - - none

SOLVED with punk2x method.

here is the log and the screenshot after I tried punk2x method, in case you're curious

15/054/2013 01:54:39 - INFO - <- This level is successfully initialized
15/054/2013 01:54:39 - INFO - Flashtool Version 0.9.10.1 built on 2013-01-09 19:49:47
15/054/2013 01:54:39 - INFO - You can drag and drop ftf files here to start flashing them
15/054/2013 01:54:43 - INFO - Device disconnected
15/054/2013 01:54:47 - INFO - Device connected in fastboot mode
15/054/2013 01:54:55 - INFO - List of connected devices (Device Id) :
15/054/2013 01:54:55 - INFO - - USB\VID_0FCE&PID_0DDE\BX902NV2B6&ZLP	Driver installed : true
15/054/2013 01:54:55 - INFO - List of ADB devices :
15/054/2013 01:54:55 - INFO - - none
15/054/2013 01:54:55 - INFO - List of fastboot devices :
15/054/2013 01:54:55 - INFO - - none
15/054/2013 01:54:59 - INFO - Launching Fastboot Toolbox 1.0 by DooMLoRD
15/054/2013 01:54:59 - INFO - Device Status: FASTBOOT mode
15/055/2013 01:55:10 - INFO - Selected kernel (boot.img or kernel.sin): E:\Dropbox\Xperia Mini Pro\Kernel\minipro_mesa_hybrid_v4.3.img
15/055/2013 01:55:10 - INFO - Flashing selected kernel
15/055/2013 01:55:13 - INFO - sending 'boot' (10072 KB)...
15/055/2013 01:55:13 - INFO - (bootloader) USB download speed was 9342kB/s
15/055/2013 01:55:13 - INFO - OKAY [ 1.116s]
15/055/2013 01:55:13 - INFO - writing 'boot'...
15/055/2013 01:55:13 - INFO - (bootloader) Download buffer format: boot IMG
15/055/2013 01:55:13 - INFO - (bootloader) Flash of partition 'boot' requested
15/055/2013 01:55:13 - INFO - (bootloader) S1 partID 0x00000003, block 0x00000280-0x000002e3
15/055/2013 01:55:13 - INFO - (bootloader) Erase operation complete, 0 bad blocks encountered
15/055/2013 01:55:13 - INFO - (bootloader) Flashing...
15/055/2013 01:55:13 - INFO - (bootloader) Flash operation complete
15/055/2013 01:55:13 - INFO - OKAY [ 1.942s]
15/055/2013 01:55:13 - INFO - finished. total time: 3.058s
15/055/2013 01:55:13 - INFO - FASTBOOT Output:
sending 'boot' (10072 KB)...
(bootloader) USB download speed was 9342kB/s
OKAY [ 1.116s]
writing 'boot'...
(bootloader) Download buffer format: boot IMG
(bootloader) Flash of partition 'boot' requested
(bootloader) S1 partID 0x00000003, block 0x00000280-0x000002e3
(bootloader) Erase operation complete, 0 bad blocks encountered
(bootloader) Flashing...
(bootloader) Flash operation complete
OKAY [ 1.942s]
finished. total time: 3.058s

15/055/2013 01:55:13 - INFO - Please check the log before rebooting into system
15/055/2013 01:55:16 - INFO - Finished Fastboot Toolbox

and yes, the problem from the previous problem that both I & monjovega had was not working fastboot.

the flashmode itself leave no problem.