Sony Xperia Z3 SO-01G Cant flash??

At least, I think that's the problem. After trying to flash a newer SO-01G_NTT DoCoMo JP_1290-5930_23.1.B.1.160 on my phone with Flashtool (v0.9.19.1) Windows 8.1, all it does is boot to the SONY logo, then proceeds to say "The software update failed. Make sure that your phone is connected to the computer and try again." This only happens again and again afterwards..

During the flashing process, it seems all fine and dandy until it comes to the system.sin part, finishes and results in an error. It seems to me that according to the log from Flashtool, the program is loading it into the phone but the phone is rejecting it or something? Could it be that there is not enough space left on the phone to flash another rom?

Writing packet to phone
10/002/2015 00:02:56 - DEBUG - (USBFlashWin32.java:47) - OUT : CommandID : 6 / Flags : false,true,true / Data length : 524288 / Data CRC32 : [21, C7, 4A, E0]
10/002/2015 00:02:56 - DEBUG - (USBFlashWin32.java:58) - Reading packet from phone
10/002/2015 00:02:56 - DEBUG - (USBFlashWin32.java:64) - IN : CommandID : 6 / Flags : false,false,false / Data length : 0 / Data CRC32 : [00, 00, 00, 00]

Ive tried alternatives to this Flashtool, including Emma and PC Companion. But because the phone naturally has a locked bootloader that cant be unlocked due to the previous carriers restrictions (NTT DoCoMo).

Thanks in advance?! :fingers-crossed: :)