Xperia M trying to go back to stock rom

I've installed the Cyanogenmod, but it doesn't detect the simcard, so I would like to go back to stock rom.
I have the flashtool of course, and I've found a 4.3-boot.img which should be a good recover img, and that has been placed on the device with the fastboot command
I've also downloaded the C1905_15.1.A.1.9_GLOBAL-INA.ftf
But when I try to use the flashtool to put the ftf file on it, I get these messages:
10/053/2015 13:53:02 - INFO - Selected Bundle for Sony Xperia M (C1905). FW release : 15.1.A.1.9. Customization : GLOBAL-kuswosplakuk
10/053/2015 13:53:02 - INFO - Preparing files for flashing
10/053/2015 13:53:07 - INFO - Please connect your device into flashmode.
10/053/2015 13:53:15 - INFO - Device disconnected
10/053/2015 13:53:27 - INFO - Device connected in flash mode
10/053/2015 13:53:28 - INFO - Opening device for R/W
10/053/2015 13:53:28 - INFO - Reading device information
10/053/2015 13:53:28 - INFO - Phone ready for flashmode operations.
10/053/2015 13:53:28 - INFO - Opening TA partition 2
10/053/2015 13:53:28 - INFO - Current device : Unknown: May 9 2014/12:58:25 - YT910CME8S - Unknown: May 9 2014/12:58:25 - Unknown: May 9 2014/12:58:25 - Unknown: May 9 2014/12:58:25
10/053/2015 13:53:28 - INFO - Closing TA partition
10/053/2015 13:53:28 - INFO - Start Flashing
10/053/2015 13:53:28 - INFO - Processing loader.sin
10/053/2015 13:53:28 - INFO - Checking header
10/053/2015 13:53:28 - INFO - Flashing data
10/053/2015 13:53:28 - INFO - Loader : S1_Root_dbe9 - Version : loader_MSM8X30_10 / Boot version : S1_Boot_MSM_8227_5 / Bootloader status : ROOTED
10/053/2015 13:53:28 - INFO - Transfer buffer size : 262144
10/053/2015 13:53:28 - WARN - File simlock.ta is ignored
10/053/2015 13:53:28 - INFO - You must have the according fsc script to flash this device.
10/053/2015 13:53:28 - INFO - Flashing finished.
10/053/2015 13:53:28 - INFO - Please unplug and start your phone
10/053/2015 13:53:28 - INFO - For flashtool, Unknown Sources and Debugging must be checked in phone settings
And when booting the device it shows the SONY logo, and then goes to black screen.